src/HOL/Decision_Procs/Approximation.thy
author huffman
Sat Aug 20 15:54:26 2011 -0700 (2011-08-20)
changeset 44349 f057535311c5
parent 44306 33572a766836
child 44568 e6f291cb5810
permissions -rw-r--r--
remove redundant lemma real_0_le_divide_iff in favor or zero_le_divide_iff
hoelzl@40881
     1
(* Author:     Johannes Hoelzl, TU Muenchen
hoelzl@40881
     2
   Coercions removed by Dmitriy Traytel *)
wenzelm@30122
     3
wenzelm@30886
     4
header {* Prove Real Valued Inequalities by Computation *}
wenzelm@30122
     5
wenzelm@40892
     6
theory Approximation
wenzelm@41413
     7
imports
wenzelm@41413
     8
  Complex_Main
wenzelm@41413
     9
  "~~/src/HOL/Library/Float"
wenzelm@41413
    10
  "~~/src/HOL/Library/Reflection"
wenzelm@41413
    11
  "~~/src/HOL/Decision_Procs/Dense_Linear_Order"
wenzelm@41413
    12
  "~~/src/HOL/Library/Efficient_Nat"
hoelzl@29805
    13
begin
hoelzl@29805
    14
hoelzl@29805
    15
section "Horner Scheme"
hoelzl@29805
    16
hoelzl@29805
    17
subsection {* Define auxiliary helper @{text horner} function *}
hoelzl@29805
    18
hoelzl@31098
    19
primrec horner :: "(nat \<Rightarrow> nat) \<Rightarrow> (nat \<Rightarrow> nat \<Rightarrow> nat) \<Rightarrow> nat \<Rightarrow> nat \<Rightarrow> nat \<Rightarrow> real \<Rightarrow> real" where
hoelzl@29805
    20
"horner F G 0 i k x       = 0" |
hoelzl@40881
    21
"horner F G (Suc n) i k x = 1 / k - x * horner F G n (F i) (G i k) x"
hoelzl@29805
    22
hoelzl@29805
    23
lemma horner_schema': fixes x :: real  and a :: "nat \<Rightarrow> real"
hoelzl@29805
    24
  shows "a 0 - x * (\<Sum> i=0..<n. (-1)^i * a (Suc i) * x^i) = (\<Sum> i=0..<Suc n. (-1)^i * a i * x^i)"
hoelzl@29805
    25
proof -
hoelzl@29805
    26
  have shift_pow: "\<And>i. - (x * ((-1)^i * a (Suc i) * x ^ i)) = (-1)^(Suc i) * a (Suc i) * x ^ (Suc i)" by auto
haftmann@37887
    27
  show ?thesis unfolding setsum_right_distrib shift_pow diff_minus setsum_negf[symmetric] setsum_head_upt_Suc[OF zero_less_Suc]
hoelzl@29805
    28
    setsum_reindex[OF inj_Suc, unfolded comp_def, symmetric, of "\<lambda> n. (-1)^n  *a n * x^n"] by auto
hoelzl@29805
    29
qed
hoelzl@29805
    30
hoelzl@29805
    31
lemma horner_schema: fixes f :: "nat \<Rightarrow> nat" and G :: "nat \<Rightarrow> nat \<Rightarrow> nat" and F :: "nat \<Rightarrow> nat"
haftmann@30971
    32
  assumes f_Suc: "\<And>n. f (Suc n) = G ((F ^^ n) s) (f n)"
hoelzl@40881
    33
  shows "horner F G n ((F ^^ j') s) (f j') x = (\<Sum> j = 0..< n. -1 ^ j * (1 / (f (j' + j))) * x ^ j)"
hoelzl@29805
    34
proof (induct n arbitrary: i k j')
hoelzl@29805
    35
  case (Suc n)
hoelzl@29805
    36
hoelzl@29805
    37
  show ?case unfolding horner.simps Suc[where j'="Suc j'", unfolded funpow.simps comp_def f_Suc]
hoelzl@40881
    38
    using horner_schema'[of "\<lambda> j. 1 / (f (j' + j))"] by auto
hoelzl@29805
    39
qed auto
hoelzl@29805
    40
hoelzl@29805
    41
lemma horner_bounds':
hoelzl@40881
    42
  fixes lb :: "nat \<Rightarrow> nat \<Rightarrow> nat \<Rightarrow> float \<Rightarrow> float" and ub :: "nat \<Rightarrow> nat \<Rightarrow> nat \<Rightarrow> float \<Rightarrow> float"
hoelzl@31098
    43
  assumes "0 \<le> real x" and f_Suc: "\<And>n. f (Suc n) = G ((F ^^ n) s) (f n)"
hoelzl@29805
    44
  and lb_0: "\<And> i k x. lb 0 i k x = 0"
hoelzl@40881
    45
  and lb_Suc: "\<And> n i k x. lb (Suc n) i k x = lapprox_rat prec 1 k - x * (ub n (F i) (G i k) x)"
hoelzl@29805
    46
  and ub_0: "\<And> i k x. ub 0 i k x = 0"
hoelzl@40881
    47
  and ub_Suc: "\<And> n i k x. ub (Suc n) i k x = rapprox_rat prec 1 k - x * (lb n (F i) (G i k) x)"
hoelzl@40881
    48
  shows "(lb n ((F ^^ j') s) (f j') x) \<le> horner F G n ((F ^^ j') s) (f j') x \<and>
hoelzl@40881
    49
         horner F G n ((F ^^ j') s) (f j') x \<le> (ub n ((F ^^ j') s) (f j') x)"
hoelzl@29805
    50
  (is "?lb n j' \<le> ?horner n j' \<and> ?horner n j' \<le> ?ub n j'")
hoelzl@29805
    51
proof (induct n arbitrary: j')
hoelzl@29805
    52
  case 0 thus ?case unfolding lb_0 ub_0 horner.simps by auto
hoelzl@29805
    53
next
hoelzl@29805
    54
  case (Suc n)
haftmann@37887
    55
  have "?lb (Suc n) j' \<le> ?horner (Suc n) j'" unfolding lb_Suc ub_Suc horner.simps real_of_float_sub diff_minus
hoelzl@29805
    56
  proof (rule add_mono)
hoelzl@40881
    57
    show "(lapprox_rat prec 1 (f j')) \<le> 1 / (f j')" using lapprox_rat[of prec 1  "f j'"] by auto
hoelzl@31098
    58
    from Suc[where j'="Suc j'", unfolded funpow.simps comp_def f_Suc, THEN conjunct2] `0 \<le> real x`
hoelzl@40881
    59
    show "- real (x * ub n (F ((F ^^ j') s)) (G ((F ^^ j') s) (f j')) x) \<le>
hoelzl@40881
    60
          - (x * horner F G n (F ((F ^^ j') s)) (G ((F ^^ j') s) (f j')) x)"
hoelzl@31098
    61
      unfolding real_of_float_mult neg_le_iff_le by (rule mult_left_mono)
hoelzl@29805
    62
  qed
haftmann@37887
    63
  moreover have "?horner (Suc n) j' \<le> ?ub (Suc n) j'" unfolding ub_Suc ub_Suc horner.simps real_of_float_sub diff_minus
hoelzl@29805
    64
  proof (rule add_mono)
hoelzl@40881
    65
    show "1 / (f j') \<le> (rapprox_rat prec 1 (f j'))" using rapprox_rat[of 1 "f j'" prec] by auto
hoelzl@31098
    66
    from Suc[where j'="Suc j'", unfolded funpow.simps comp_def f_Suc, THEN conjunct1] `0 \<le> real x`
hoelzl@40881
    67
    show "- (x * horner F G n (F ((F ^^ j') s)) (G ((F ^^ j') s) (f j')) x) \<le>
hoelzl@31098
    68
          - real (x * lb n (F ((F ^^ j') s)) (G ((F ^^ j') s) (f j')) x)"
hoelzl@31098
    69
      unfolding real_of_float_mult neg_le_iff_le by (rule mult_left_mono)
hoelzl@29805
    70
  qed
hoelzl@29805
    71
  ultimately show ?case by blast
hoelzl@29805
    72
qed
hoelzl@29805
    73
hoelzl@29805
    74
subsection "Theorems for floating point functions implementing the horner scheme"
hoelzl@29805
    75
hoelzl@29805
    76
text {*
hoelzl@29805
    77
hoelzl@29805
    78
Here @{term_type "f :: nat \<Rightarrow> nat"} is the sequence defining the Taylor series, the coefficients are
hoelzl@29805
    79
all alternating and reciprocs. We use @{term G} and @{term F} to describe the computation of @{term f}.
hoelzl@29805
    80
hoelzl@29805
    81
*}
hoelzl@29805
    82
hoelzl@29805
    83
lemma horner_bounds: fixes F :: "nat \<Rightarrow> nat" and G :: "nat \<Rightarrow> nat \<Rightarrow> nat"
hoelzl@31098
    84
  assumes "0 \<le> real x" and f_Suc: "\<And>n. f (Suc n) = G ((F ^^ n) s) (f n)"
hoelzl@29805
    85
  and lb_0: "\<And> i k x. lb 0 i k x = 0"
hoelzl@40881
    86
  and lb_Suc: "\<And> n i k x. lb (Suc n) i k x = lapprox_rat prec 1 k - x * (ub n (F i) (G i k) x)"
hoelzl@29805
    87
  and ub_0: "\<And> i k x. ub 0 i k x = 0"
hoelzl@40881
    88
  and ub_Suc: "\<And> n i k x. ub (Suc n) i k x = rapprox_rat prec 1 k - x * (lb n (F i) (G i k) x)"
hoelzl@40881
    89
  shows "(lb n ((F ^^ j') s) (f j') x) \<le> (\<Sum>j=0..<n. -1 ^ j * (1 / (f (j' + j))) * (x ^ j))" (is "?lb") and
hoelzl@40881
    90
    "(\<Sum>j=0..<n. -1 ^ j * (1 / (f (j' + j))) * (x ^ j)) \<le> (ub n ((F ^^ j') s) (f j') x)" (is "?ub")
hoelzl@29805
    91
proof -
hoelzl@31809
    92
  have "?lb  \<and> ?ub"
hoelzl@31098
    93
    using horner_bounds'[where lb=lb, OF `0 \<le> real x` f_Suc lb_0 lb_Suc ub_0 ub_Suc]
hoelzl@29805
    94
    unfolding horner_schema[where f=f, OF f_Suc] .
hoelzl@29805
    95
  thus "?lb" and "?ub" by auto
hoelzl@29805
    96
qed
hoelzl@29805
    97
hoelzl@29805
    98
lemma horner_bounds_nonpos: fixes F :: "nat \<Rightarrow> nat" and G :: "nat \<Rightarrow> nat \<Rightarrow> nat"
hoelzl@31098
    99
  assumes "real x \<le> 0" and f_Suc: "\<And>n. f (Suc n) = G ((F ^^ n) s) (f n)"
hoelzl@29805
   100
  and lb_0: "\<And> i k x. lb 0 i k x = 0"
hoelzl@40881
   101
  and lb_Suc: "\<And> n i k x. lb (Suc n) i k x = lapprox_rat prec 1 k + x * (ub n (F i) (G i k) x)"
hoelzl@29805
   102
  and ub_0: "\<And> i k x. ub 0 i k x = 0"
hoelzl@40881
   103
  and ub_Suc: "\<And> n i k x. ub (Suc n) i k x = rapprox_rat prec 1 k + x * (lb n (F i) (G i k) x)"
hoelzl@40881
   104
  shows "(lb n ((F ^^ j') s) (f j') x) \<le> (\<Sum>j=0..<n. (1 / (f (j' + j))) * real x ^ j)" (is "?lb") and
hoelzl@40881
   105
    "(\<Sum>j=0..<n. (1 / (f (j' + j))) * real x ^ j) \<le> (ub n ((F ^^ j') s) (f j') x)" (is "?ub")
hoelzl@29805
   106
proof -
hoelzl@29805
   107
  { fix x y z :: float have "x - y * z = x + - y * z"
haftmann@30968
   108
      by (cases x, cases y, cases z, simp add: plus_float.simps minus_float_def uminus_float.simps times_float.simps algebra_simps)
hoelzl@29805
   109
  } note diff_mult_minus = this
hoelzl@29805
   110
hoelzl@29805
   111
  { fix x :: float have "- (- x) = x" by (cases x, auto simp add: uminus_float.simps) } note minus_minus = this
hoelzl@29805
   112
hoelzl@40881
   113
  have move_minus: "(-x) = -1 * real x" by auto (* coercion "inside" is necessary *)
hoelzl@40881
   114
hoelzl@40881
   115
  have sum_eq: "(\<Sum>j=0..<n. (1 / (f (j' + j))) * real x ^ j) =
hoelzl@40881
   116
    (\<Sum>j = 0..<n. -1 ^ j * (1 / (f (j' + j))) * real (- x) ^ j)"
hoelzl@29805
   117
  proof (rule setsum_cong, simp)
hoelzl@29805
   118
    fix j assume "j \<in> {0 ..< n}"
hoelzl@40881
   119
    show "1 / (f (j' + j)) * real x ^ j = -1 ^ j * (1 / (f (j' + j))) * real (- x) ^ j"
huffman@36778
   120
      unfolding move_minus power_mult_distrib mult_assoc[symmetric]
huffman@36778
   121
      unfolding mult_commute unfolding mult_assoc[of "-1 ^ j", symmetric] power_mult_distrib[symmetric]
hoelzl@29805
   122
      by auto
hoelzl@29805
   123
  qed
hoelzl@29805
   124
hoelzl@31098
   125
  have "0 \<le> real (-x)" using assms by auto
hoelzl@29805
   126
  from horner_bounds[where G=G and F=F and f=f and s=s and prec=prec
hoelzl@29805
   127
    and lb="\<lambda> n i k x. lb n i k (-x)" and ub="\<lambda> n i k x. ub n i k (-x)", unfolded lb_Suc ub_Suc diff_mult_minus,
hoelzl@29805
   128
    OF this f_Suc lb_0 refl ub_0 refl]
hoelzl@29805
   129
  show "?lb" and "?ub" unfolding minus_minus sum_eq
hoelzl@29805
   130
    by auto
hoelzl@29805
   131
qed
hoelzl@29805
   132
hoelzl@29805
   133
subsection {* Selectors for next even or odd number *}
hoelzl@29805
   134
hoelzl@29805
   135
text {*
hoelzl@29805
   136
hoelzl@29805
   137
The horner scheme computes alternating series. To get the upper and lower bounds we need to
hoelzl@29805
   138
guarantee to access a even or odd member. To do this we use @{term get_odd} and @{term get_even}.
hoelzl@29805
   139
hoelzl@29805
   140
*}
hoelzl@29805
   141
hoelzl@29805
   142
definition get_odd :: "nat \<Rightarrow> nat" where
hoelzl@29805
   143
  "get_odd n = (if odd n then n else (Suc n))"
hoelzl@29805
   144
hoelzl@29805
   145
definition get_even :: "nat \<Rightarrow> nat" where
hoelzl@29805
   146
  "get_even n = (if even n then n else (Suc n))"
hoelzl@29805
   147
hoelzl@29805
   148
lemma get_odd[simp]: "odd (get_odd n)" unfolding get_odd_def by (cases "odd n", auto)
hoelzl@29805
   149
lemma get_even[simp]: "even (get_even n)" unfolding get_even_def by (cases "even n", auto)
hoelzl@29805
   150
lemma get_odd_ex: "\<exists> k. Suc k = get_odd n \<and> odd (Suc k)"
hoelzl@29805
   151
proof (cases "odd n")
hoelzl@29805
   152
  case True hence "0 < n" by (rule odd_pos)
hoelzl@31467
   153
  from gr0_implies_Suc[OF this] obtain k where "Suc k = n" by auto
hoelzl@29805
   154
  thus ?thesis unfolding get_odd_def if_P[OF True] using True[unfolded `Suc k = n`[symmetric]] by blast
hoelzl@29805
   155
next
hoelzl@29805
   156
  case False hence "odd (Suc n)" by auto
hoelzl@29805
   157
  thus ?thesis unfolding get_odd_def if_not_P[OF False] by blast
hoelzl@29805
   158
qed
hoelzl@29805
   159
hoelzl@29805
   160
lemma get_even_double: "\<exists>i. get_even n = 2 * i" using get_even[unfolded even_mult_two_ex] .
hoelzl@29805
   161
lemma get_odd_double: "\<exists>i. get_odd n = 2 * i + 1" using get_odd[unfolded odd_Suc_mult_two_ex] by auto
hoelzl@29805
   162
hoelzl@29805
   163
section "Power function"
hoelzl@29805
   164
hoelzl@29805
   165
definition float_power_bnds :: "nat \<Rightarrow> float \<Rightarrow> float \<Rightarrow> float * float" where
hoelzl@29805
   166
"float_power_bnds n l u = (if odd n \<or> 0 < l then (l ^ n, u ^ n)
hoelzl@29805
   167
                      else if u < 0         then (u ^ n, l ^ n)
hoelzl@29805
   168
                                            else (0, (max (-l) u) ^ n))"
hoelzl@29805
   169
hoelzl@40881
   170
lemma float_power_bnds: fixes x :: real
hoelzl@40881
   171
  assumes "(l1, u1) = float_power_bnds n l u" and "x \<in> {l .. u}"
hoelzl@40881
   172
  shows "x ^ n \<in> {l1..u1}"
hoelzl@29805
   173
proof (cases "even n")
hoelzl@31467
   174
  case True
hoelzl@29805
   175
  show ?thesis
hoelzl@29805
   176
  proof (cases "0 < l")
hoelzl@31098
   177
    case True hence "odd n \<or> 0 < l" and "0 \<le> real l" unfolding less_float_def by auto
hoelzl@29805
   178
    have u1: "u1 = u ^ n" and l1: "l1 = l ^ n" using assms unfolding float_power_bnds_def if_P[OF `odd n \<or> 0 < l`] by auto
hoelzl@40881
   179
    have "real l ^ n \<le> x ^ n" and "x ^ n \<le> real u ^ n " using `0 \<le> real l` and assms unfolding atLeastAtMost_iff using power_mono[of l x] power_mono[of x u] by auto
hoelzl@29805
   180
    thus ?thesis using assms `0 < l` unfolding atLeastAtMost_iff l1 u1 float_power less_float_def by auto
hoelzl@29805
   181
  next
hoelzl@29805
   182
    case False hence P: "\<not> (odd n \<or> 0 < l)" using `even n` by auto
hoelzl@29805
   183
    show ?thesis
hoelzl@29805
   184
    proof (cases "u < 0")
hoelzl@31098
   185
      case True hence "0 \<le> - real u" and "- real u \<le> - x" and "0 \<le> - x" and "-x \<le> - real l" using assms unfolding less_float_def by auto
hoelzl@31809
   186
      hence "real u ^ n \<le> x ^ n" and "x ^ n \<le> real l ^ n" using power_mono[of  "-x" "-real l" n] power_mono[of "-real u" "-x" n]
wenzelm@32960
   187
        unfolding power_minus_even[OF `even n`] by auto
hoelzl@29805
   188
      moreover have u1: "u1 = l ^ n" and l1: "l1 = u ^ n" using assms unfolding float_power_bnds_def if_not_P[OF P] if_P[OF True] by auto
hoelzl@29805
   189
      ultimately show ?thesis using float_power by auto
hoelzl@29805
   190
    next
hoelzl@31467
   191
      case False
hoelzl@31098
   192
      have "\<bar>x\<bar> \<le> real (max (-l) u)"
hoelzl@29805
   193
      proof (cases "-l \<le> u")
wenzelm@32960
   194
        case True thus ?thesis unfolding max_def if_P[OF True] using assms unfolding le_float_def by auto
hoelzl@29805
   195
      next
wenzelm@32960
   196
        case False thus ?thesis unfolding max_def if_not_P[OF False] using assms unfolding le_float_def by auto
hoelzl@29805
   197
      qed
hoelzl@31098
   198
      hence x_abs: "\<bar>x\<bar> \<le> \<bar>real (max (-l) u)\<bar>" by auto
hoelzl@29805
   199
      have u1: "u1 = (max (-l) u) ^ n" and l1: "l1 = 0" using assms unfolding float_power_bnds_def if_not_P[OF P] if_not_P[OF False] by auto
hoelzl@29805
   200
      show ?thesis unfolding atLeastAtMost_iff l1 u1 float_power using zero_le_even_power[OF `even n`] power_mono_even[OF `even n` x_abs] by auto
hoelzl@29805
   201
    qed
hoelzl@29805
   202
  qed
hoelzl@29805
   203
next
hoelzl@29805
   204
  case False hence "odd n \<or> 0 < l" by auto
hoelzl@29805
   205
  have u1: "u1 = u ^ n" and l1: "l1 = l ^ n" using assms unfolding float_power_bnds_def if_P[OF `odd n \<or> 0 < l`] by auto
hoelzl@31098
   206
  have "real l ^ n \<le> x ^ n" and "x ^ n \<le> real u ^ n " using assms unfolding atLeastAtMost_iff using power_mono_odd[OF False] by auto
hoelzl@29805
   207
  thus ?thesis unfolding atLeastAtMost_iff l1 u1 float_power less_float_def by auto
hoelzl@29805
   208
qed
hoelzl@29805
   209
hoelzl@40881
   210
lemma bnds_power: "\<forall> (x::real) l u. (l1, u1) = float_power_bnds n l u \<and> x \<in> {l .. u} \<longrightarrow> l1 \<le> x ^ n \<and> x ^ n \<le> u1"
hoelzl@29805
   211
  using float_power_bnds by auto
hoelzl@29805
   212
hoelzl@29805
   213
section "Square root"
hoelzl@29805
   214
hoelzl@29805
   215
text {*
hoelzl@29805
   216
hoelzl@29805
   217
The square root computation is implemented as newton iteration. As first first step we use the
hoelzl@29805
   218
nearest power of two greater than the square root.
hoelzl@29805
   219
hoelzl@29805
   220
*}
hoelzl@29805
   221
hoelzl@29805
   222
fun sqrt_iteration :: "nat \<Rightarrow> nat \<Rightarrow> float \<Rightarrow> float" where
hoelzl@29805
   223
"sqrt_iteration prec 0 (Float m e) = Float 1 ((e + bitlen m) div 2 + 1)" |
hoelzl@31467
   224
"sqrt_iteration prec (Suc m) x = (let y = sqrt_iteration prec m x
hoelzl@29805
   225
                                  in Float 1 -1 * (y + float_divr prec x y))"
hoelzl@29805
   226
hoelzl@31467
   227
function ub_sqrt lb_sqrt :: "nat \<Rightarrow> float \<Rightarrow> float" where
hoelzl@31467
   228
"ub_sqrt prec x = (if 0 < x then (sqrt_iteration prec prec x)
hoelzl@31467
   229
              else if x < 0 then - lb_sqrt prec (- x)
hoelzl@31467
   230
                            else 0)" |
hoelzl@31467
   231
"lb_sqrt prec x = (if 0 < x then (float_divl prec x (sqrt_iteration prec prec x))
hoelzl@31467
   232
              else if x < 0 then - ub_sqrt prec (- x)
hoelzl@31467
   233
                            else 0)"
hoelzl@31467
   234
by pat_completeness auto
hoelzl@31467
   235
termination by (relation "measure (\<lambda> v. let (prec, x) = sum_case id id v in (if x < 0 then 1 else 0))", auto simp add: less_float_def)
hoelzl@29805
   236
hoelzl@31467
   237
declare lb_sqrt.simps[simp del]
hoelzl@31467
   238
declare ub_sqrt.simps[simp del]
hoelzl@29805
   239
hoelzl@29805
   240
lemma sqrt_ub_pos_pos_1:
hoelzl@29805
   241
  assumes "sqrt x < b" and "0 < b" and "0 < x"
hoelzl@29805
   242
  shows "sqrt x < (b + x / b)/2"
hoelzl@29805
   243
proof -
hoelzl@29805
   244
  from assms have "0 < (b - sqrt x) ^ 2 " by simp
hoelzl@29805
   245
  also have "\<dots> = b ^ 2 - 2 * b * sqrt x + (sqrt x) ^ 2" by algebra
hoelzl@29805
   246
  also have "\<dots> = b ^ 2 - 2 * b * sqrt x + x" using assms by (simp add: real_sqrt_pow2)
hoelzl@29805
   247
  finally have "0 < b ^ 2 - 2 * b * sqrt x + x" by assumption
hoelzl@29805
   248
  hence "0 < b / 2 - sqrt x + x / (2 * b)" using assms
hoelzl@29805
   249
    by (simp add: field_simps power2_eq_square)
hoelzl@29805
   250
  thus ?thesis by (simp add: field_simps)
hoelzl@29805
   251
qed
hoelzl@29805
   252
hoelzl@31098
   253
lemma sqrt_iteration_bound: assumes "0 < real x"
hoelzl@40881
   254
  shows "sqrt x < (sqrt_iteration prec n x)"
hoelzl@29805
   255
proof (induct n)
hoelzl@29805
   256
  case 0
hoelzl@29805
   257
  show ?case
hoelzl@29805
   258
  proof (cases x)
hoelzl@29805
   259
    case (Float m e)
hoelzl@29805
   260
    hence "0 < m" using float_pos_m_pos[unfolded less_float_def] assms by auto
hoelzl@40881
   261
    hence "0 < sqrt m" by auto
hoelzl@40881
   262
hoelzl@40881
   263
    have int_nat_bl: "(nat (bitlen m)) = bitlen m" using bitlen_ge0 by auto
hoelzl@40881
   264
hoelzl@40881
   265
    have "x = (m / 2^nat (bitlen m)) * pow2 (e + (nat (bitlen m)))"
hoelzl@31098
   266
      unfolding pow2_add pow2_int Float real_of_float_simp by auto
hoelzl@40881
   267
    also have "\<dots> < 1 * pow2 (e + nat (bitlen m))"
hoelzl@29805
   268
    proof (rule mult_strict_right_mono, auto)
hoelzl@31467
   269
      show "real m < 2^nat (bitlen m)" using bitlen_bounds[OF `0 < m`, THEN conjunct2]
wenzelm@32960
   270
        unfolding real_of_int_less_iff[of m, symmetric] by auto
hoelzl@29805
   271
    qed
hoelzl@40881
   272
    finally have "sqrt x < sqrt (pow2 (e + bitlen m))" unfolding int_nat_bl by auto
hoelzl@29805
   273
    also have "\<dots> \<le> pow2 ((e + bitlen m) div 2 + 1)"
hoelzl@29805
   274
    proof -
hoelzl@29805
   275
      let ?E = "e + bitlen m"
hoelzl@29805
   276
      have E_mod_pow: "pow2 (?E mod 2) < 4"
hoelzl@29805
   277
      proof (cases "?E mod 2 = 1")
wenzelm@32960
   278
        case True thus ?thesis by auto
hoelzl@29805
   279
      next
wenzelm@32960
   280
        case False
wenzelm@32960
   281
        have "0 \<le> ?E mod 2" by auto
wenzelm@32960
   282
        have "?E mod 2 < 2" by auto
wenzelm@32960
   283
        from this[THEN zless_imp_add1_zle]
wenzelm@32960
   284
        have "?E mod 2 \<le> 0" using False by auto
wenzelm@32960
   285
        from xt1(5)[OF `0 \<le> ?E mod 2` this]
wenzelm@32960
   286
        show ?thesis by auto
hoelzl@29805
   287
      qed
hoelzl@29805
   288
      hence "sqrt (pow2 (?E mod 2)) < sqrt (2 * 2)" by auto
hoelzl@29805
   289
      hence E_mod_pow: "sqrt (pow2 (?E mod 2)) < 2" unfolding real_sqrt_abs2 by auto
hoelzl@29805
   290
hoelzl@29805
   291
      have E_eq: "pow2 ?E = pow2 (?E div 2 + ?E div 2 + ?E mod 2)" by auto
hoelzl@29805
   292
      have "sqrt (pow2 ?E) = sqrt (pow2 (?E div 2) * pow2 (?E div 2) * pow2 (?E mod 2))"
wenzelm@32960
   293
        unfolding E_eq unfolding pow2_add ..
hoelzl@29805
   294
      also have "\<dots> = pow2 (?E div 2) * sqrt (pow2 (?E mod 2))"
wenzelm@32960
   295
        unfolding real_sqrt_mult[of _ "pow2 (?E mod 2)"] real_sqrt_abs2 by auto
hoelzl@31467
   296
      also have "\<dots> < pow2 (?E div 2) * 2"
wenzelm@32960
   297
        by (rule mult_strict_left_mono, auto intro: E_mod_pow)
hoelzl@29805
   298
      also have "\<dots> = pow2 (?E div 2 + 1)" unfolding zadd_commute[of _ 1] pow2_add1 by auto
hoelzl@29805
   299
      finally show ?thesis by auto
hoelzl@29805
   300
    qed
hoelzl@31467
   301
    finally show ?thesis
hoelzl@31098
   302
      unfolding Float sqrt_iteration.simps real_of_float_simp by auto
hoelzl@29805
   303
  qed
hoelzl@29805
   304
next
hoelzl@29805
   305
  case (Suc n)
hoelzl@29805
   306
  let ?b = "sqrt_iteration prec n x"
hoelzl@40881
   307
  have "0 < sqrt x" using `0 < real x` by auto
hoelzl@31098
   308
  also have "\<dots> < real ?b" using Suc .
hoelzl@40881
   309
  finally have "sqrt x < (?b + x / ?b)/2" using sqrt_ub_pos_pos_1[OF Suc _ `0 < real x`] by auto
hoelzl@40881
   310
  also have "\<dots> \<le> (?b + (float_divr prec x ?b))/2" by (rule divide_right_mono, auto simp add: float_divr)
hoelzl@40881
   311
  also have "\<dots> = (Float 1 -1) * (?b + (float_divr prec x ?b))" by auto
hoelzl@31098
   312
  finally show ?case unfolding sqrt_iteration.simps Let_def real_of_float_mult real_of_float_add right_distrib .
hoelzl@29805
   313
qed
hoelzl@29805
   314
hoelzl@31098
   315
lemma sqrt_iteration_lower_bound: assumes "0 < real x"
hoelzl@31098
   316
  shows "0 < real (sqrt_iteration prec n x)" (is "0 < ?sqrt")
hoelzl@29805
   317
proof -
hoelzl@40881
   318
  have "0 < sqrt x" using assms by auto
hoelzl@29805
   319
  also have "\<dots> < ?sqrt" using sqrt_iteration_bound[OF assms] .
hoelzl@29805
   320
  finally show ?thesis .
hoelzl@29805
   321
qed
hoelzl@29805
   322
hoelzl@31098
   323
lemma lb_sqrt_lower_bound: assumes "0 \<le> real x"
hoelzl@31467
   324
  shows "0 \<le> real (lb_sqrt prec x)"
hoelzl@29805
   325
proof (cases "0 < x")
hoelzl@31098
   326
  case True hence "0 < real x" and "0 \<le> x" using `0 \<le> real x` unfolding less_float_def le_float_def by auto
hoelzl@31809
   327
  hence "0 < sqrt_iteration prec prec x" unfolding less_float_def using sqrt_iteration_lower_bound by auto
hoelzl@31098
   328
  hence "0 \<le> real (float_divl prec x (sqrt_iteration prec prec x))" using float_divl_lower_bound[OF `0 \<le> x`] unfolding le_float_def by auto
hoelzl@31467
   329
  thus ?thesis unfolding lb_sqrt.simps using True by auto
hoelzl@29805
   330
next
hoelzl@31098
   331
  case False with `0 \<le> real x` have "real x = 0" unfolding less_float_def by auto
hoelzl@31467
   332
  thus ?thesis unfolding lb_sqrt.simps less_float_def by auto
hoelzl@29805
   333
qed
hoelzl@29805
   334
hoelzl@31467
   335
lemma bnds_sqrt':
hoelzl@40881
   336
  shows "sqrt x \<in> {(lb_sqrt prec x) .. (ub_sqrt prec x) }"
hoelzl@31467
   337
proof -
hoelzl@31467
   338
  { fix x :: float assume "0 < x"
hoelzl@31467
   339
    hence "0 < real x" and "0 \<le> real x" unfolding less_float_def by auto
hoelzl@40881
   340
    hence sqrt_gt0: "0 < sqrt x" by auto
hoelzl@40881
   341
    hence sqrt_ub: "sqrt x < sqrt_iteration prec prec x" using sqrt_iteration_bound by auto
hoelzl@40881
   342
hoelzl@40881
   343
    have "(float_divl prec x (sqrt_iteration prec prec x)) \<le>
hoelzl@40881
   344
          x / (sqrt_iteration prec prec x)" by (rule float_divl)
hoelzl@40881
   345
    also have "\<dots> < x / sqrt x"
hoelzl@31467
   346
      by (rule divide_strict_left_mono[OF sqrt_ub `0 < real x`
hoelzl@31467
   347
               mult_pos_pos[OF order_less_trans[OF sqrt_gt0 sqrt_ub] sqrt_gt0]])
hoelzl@40881
   348
    also have "\<dots> = sqrt x"
hoelzl@40881
   349
      unfolding inverse_eq_iff_eq[of _ "sqrt x", symmetric]
wenzelm@32960
   350
                sqrt_divide_self_eq[OF `0 \<le> real x`, symmetric] by auto
hoelzl@40881
   351
    finally have "lb_sqrt prec x \<le> sqrt x"
hoelzl@31467
   352
      unfolding lb_sqrt.simps if_P[OF `0 < x`] by auto }
hoelzl@31467
   353
  note lb = this
hoelzl@31467
   354
hoelzl@31467
   355
  { fix x :: float assume "0 < x"
hoelzl@31467
   356
    hence "0 < real x" unfolding less_float_def by auto
hoelzl@40881
   357
    hence "0 < sqrt x" by auto
hoelzl@40881
   358
    hence "sqrt x < sqrt_iteration prec prec x"
hoelzl@31467
   359
      using sqrt_iteration_bound by auto
hoelzl@40881
   360
    hence "sqrt x \<le> ub_sqrt prec x"
hoelzl@31467
   361
      unfolding ub_sqrt.simps if_P[OF `0 < x`] by auto }
hoelzl@31467
   362
  note ub = this
hoelzl@31467
   363
hoelzl@31467
   364
  show ?thesis
hoelzl@31467
   365
  proof (cases "0 < x")
hoelzl@31467
   366
    case True with lb ub show ?thesis by auto
hoelzl@31467
   367
  next case False show ?thesis
hoelzl@31467
   368
  proof (cases "real x = 0")
hoelzl@31809
   369
    case True thus ?thesis
hoelzl@31467
   370
      by (auto simp add: less_float_def lb_sqrt.simps ub_sqrt.simps)
hoelzl@31467
   371
  next
hoelzl@31467
   372
    case False with `\<not> 0 < x` have "x < 0" and "0 < -x"
hoelzl@31467
   373
      by (auto simp add: less_float_def)
hoelzl@31467
   374
hoelzl@31467
   375
    with `\<not> 0 < x`
hoelzl@31467
   376
    show ?thesis using lb[OF `0 < -x`] ub[OF `0 < -x`]
hoelzl@31467
   377
      by (auto simp add: real_sqrt_minus lb_sqrt.simps ub_sqrt.simps)
hoelzl@31467
   378
  qed qed
hoelzl@29805
   379
qed
hoelzl@29805
   380
hoelzl@40881
   381
lemma bnds_sqrt: "\<forall> (x::real) lx ux. (l, u) = (lb_sqrt prec lx, ub_sqrt prec ux) \<and> x \<in> {lx .. ux} \<longrightarrow> l \<le> sqrt x \<and> sqrt x \<le> u"
hoelzl@31467
   382
proof ((rule allI) +, rule impI, erule conjE, rule conjI)
hoelzl@40881
   383
  fix x :: real fix lx ux
hoelzl@31467
   384
  assume "(l, u) = (lb_sqrt prec lx, ub_sqrt prec ux)"
hoelzl@40881
   385
    and x: "x \<in> {lx .. ux}"
hoelzl@31467
   386
  hence l: "l = lb_sqrt prec lx " and u: "u = ub_sqrt prec ux" by auto
hoelzl@29805
   387
hoelzl@40881
   388
  have "sqrt lx \<le> sqrt x" using x by auto
hoelzl@31467
   389
  from order_trans[OF _ this]
hoelzl@40881
   390
  show "l \<le> sqrt x" unfolding l using bnds_sqrt'[of lx prec] by auto
hoelzl@40881
   391
hoelzl@40881
   392
  have "sqrt x \<le> sqrt ux" using x by auto
hoelzl@31467
   393
  from order_trans[OF this]
hoelzl@40881
   394
  show "sqrt x \<le> u" unfolding u using bnds_sqrt'[of ux prec] by auto
hoelzl@29805
   395
qed
hoelzl@29805
   396
hoelzl@29805
   397
section "Arcus tangens and \<pi>"
hoelzl@29805
   398
hoelzl@29805
   399
subsection "Compute arcus tangens series"
hoelzl@29805
   400
hoelzl@29805
   401
text {*
hoelzl@29805
   402
hoelzl@29805
   403
As first step we implement the computation of the arcus tangens series. This is only valid in the range
hoelzl@29805
   404
@{term "{-1 :: real .. 1}"}. This is used to compute \<pi> and then the entire arcus tangens.
hoelzl@29805
   405
hoelzl@29805
   406
*}
hoelzl@29805
   407
hoelzl@29805
   408
fun ub_arctan_horner :: "nat \<Rightarrow> nat \<Rightarrow> nat \<Rightarrow> float \<Rightarrow> float"
hoelzl@29805
   409
and lb_arctan_horner :: "nat \<Rightarrow> nat \<Rightarrow> nat \<Rightarrow> float \<Rightarrow> float" where
hoelzl@29805
   410
  "ub_arctan_horner prec 0 k x = 0"
hoelzl@31809
   411
| "ub_arctan_horner prec (Suc n) k x =
hoelzl@40881
   412
    (rapprox_rat prec 1 k) - x * (lb_arctan_horner prec n (k + 2) x)"
hoelzl@29805
   413
| "lb_arctan_horner prec 0 k x = 0"
hoelzl@31809
   414
| "lb_arctan_horner prec (Suc n) k x =
hoelzl@40881
   415
    (lapprox_rat prec 1 k) - x * (ub_arctan_horner prec n (k + 2) x)"
hoelzl@29805
   416
hoelzl@31098
   417
lemma arctan_0_1_bounds': assumes "0 \<le> real x" "real x \<le> 1" and "even n"
hoelzl@40881
   418
  shows "arctan x \<in> {(x * lb_arctan_horner prec n 1 (x * x)) .. (x * ub_arctan_horner prec (Suc n) 1 (x * x))}"
hoelzl@29805
   419
proof -
hoelzl@40881
   420
  let "?c i" = "-1^i * (1 / (i * 2 + (1::nat)) * real x ^ (i * 2 + 1))"
hoelzl@29805
   421
  let "?S n" = "\<Sum> i=0..<n. ?c i"
hoelzl@29805
   422
hoelzl@31098
   423
  have "0 \<le> real (x * x)" by auto
hoelzl@29805
   424
  from `even n` obtain m where "2 * m = n" unfolding even_mult_two_ex by auto
hoelzl@31809
   425
hoelzl@40881
   426
  have "arctan x \<in> { ?S n .. ?S (Suc n) }"
hoelzl@31098
   427
  proof (cases "real x = 0")
hoelzl@29805
   428
    case False
hoelzl@31098
   429
    hence "0 < real x" using `0 \<le> real x` by auto
hoelzl@40881
   430
    hence prem: "0 < 1 / (0 * 2 + (1::nat)) * real x ^ (0 * 2 + 1)" by auto
hoelzl@29805
   431
hoelzl@31098
   432
    have "\<bar> real x \<bar> \<le> 1"  using `0 \<le> real x` `real x \<le> 1` by auto
hoelzl@29805
   433
    from mp[OF summable_Leibniz(2)[OF zeroseq_arctan_series[OF this] monoseq_arctan_series[OF this]] prem, THEN spec, of m, unfolded `2 * m = n`]
nipkow@31790
   434
    show ?thesis unfolding arctan_series[OF `\<bar> real x \<bar> \<le> 1`] Suc_eq_plus1  .
hoelzl@29805
   435
  qed auto
hoelzl@29805
   436
  note arctan_bounds = this[unfolded atLeastAtMost_iff]
hoelzl@29805
   437
hoelzl@29805
   438
  have F: "\<And>n. 2 * Suc n + 1 = 2 * n + 1 + 2" by auto
hoelzl@29805
   439
hoelzl@31809
   440
  note bounds = horner_bounds[where s=1 and f="\<lambda>i. 2 * i + 1" and j'=0
hoelzl@29805
   441
    and lb="\<lambda>n i k x. lb_arctan_horner prec n k x"
hoelzl@31809
   442
    and ub="\<lambda>n i k x. ub_arctan_horner prec n k x",
hoelzl@31098
   443
    OF `0 \<le> real (x*x)` F lb_arctan_horner.simps ub_arctan_horner.simps]
hoelzl@29805
   444
hoelzl@40881
   445
  { have "(x * lb_arctan_horner prec n 1 (x*x)) \<le> ?S n"
hoelzl@31098
   446
      using bounds(1) `0 \<le> real x`
huffman@36778
   447
      unfolding real_of_float_mult power_add power_one_right mult_assoc[symmetric] setsum_left_distrib[symmetric]
huffman@36778
   448
      unfolding mult_commute[where 'a=real] mult_commute[of _ "2::nat"] power_mult power2_eq_square[of "real x"]
hoelzl@29805
   449
      by (auto intro!: mult_left_mono)
hoelzl@40881
   450
    also have "\<dots> \<le> arctan x" using arctan_bounds ..
hoelzl@40881
   451
    finally have "(x * lb_arctan_horner prec n 1 (x*x)) \<le> arctan x" . }
hoelzl@29805
   452
  moreover
hoelzl@40881
   453
  { have "arctan x \<le> ?S (Suc n)" using arctan_bounds ..
hoelzl@40881
   454
    also have "\<dots> \<le> (x * ub_arctan_horner prec (Suc n) 1 (x*x))"
hoelzl@31098
   455
      using bounds(2)[of "Suc n"] `0 \<le> real x`
huffman@36778
   456
      unfolding real_of_float_mult power_add power_one_right mult_assoc[symmetric] setsum_left_distrib[symmetric]
huffman@36778
   457
      unfolding mult_commute[where 'a=real] mult_commute[of _ "2::nat"] power_mult power2_eq_square[of "real x"]
hoelzl@29805
   458
      by (auto intro!: mult_left_mono)
hoelzl@40881
   459
    finally have "arctan x \<le> (x * ub_arctan_horner prec (Suc n) 1 (x*x))" . }
hoelzl@29805
   460
  ultimately show ?thesis by auto
hoelzl@29805
   461
qed
hoelzl@29805
   462
hoelzl@31098
   463
lemma arctan_0_1_bounds: assumes "0 \<le> real x" "real x \<le> 1"
hoelzl@40881
   464
  shows "arctan x \<in> {(x * lb_arctan_horner prec (get_even n) 1 (x * x)) .. (x * ub_arctan_horner prec (get_odd n) 1 (x * x))}"
hoelzl@29805
   465
proof (cases "even n")
hoelzl@29805
   466
  case True
hoelzl@29805
   467
  obtain n' where "Suc n' = get_odd n" and "odd (Suc n')" using get_odd_ex by auto
nipkow@31148
   468
  hence "even n'" unfolding even_Suc by auto
hoelzl@40881
   469
  have "arctan x \<le> x * ub_arctan_horner prec (get_odd n) 1 (x * x)"
hoelzl@31098
   470
    unfolding `Suc n' = get_odd n`[symmetric] using arctan_0_1_bounds'[OF `0 \<le> real x` `real x \<le> 1` `even n'`] by auto
hoelzl@29805
   471
  moreover
hoelzl@40881
   472
  have "x * lb_arctan_horner prec (get_even n) 1 (x * x) \<le> arctan x"
hoelzl@31098
   473
    unfolding get_even_def if_P[OF True] using arctan_0_1_bounds'[OF `0 \<le> real x` `real x \<le> 1` `even n`] by auto
hoelzl@29805
   474
  ultimately show ?thesis by auto
hoelzl@29805
   475
next
hoelzl@29805
   476
  case False hence "0 < n" by (rule odd_pos)
hoelzl@29805
   477
  from gr0_implies_Suc[OF this] obtain n' where "n = Suc n'" ..
nipkow@31148
   478
  from False[unfolded this even_Suc]
hoelzl@29805
   479
  have "even n'" and "even (Suc (Suc n'))" by auto
hoelzl@29805
   480
  have "get_odd n = Suc n'" unfolding get_odd_def if_P[OF False] using `n = Suc n'` .
hoelzl@29805
   481
hoelzl@40881
   482
  have "arctan x \<le> x * ub_arctan_horner prec (get_odd n) 1 (x * x)"
hoelzl@31098
   483
    unfolding `get_odd n = Suc n'` using arctan_0_1_bounds'[OF `0 \<le> real x` `real x \<le> 1` `even n'`] by auto
hoelzl@29805
   484
  moreover
hoelzl@40881
   485
  have "(x * lb_arctan_horner prec (get_even n) 1 (x * x)) \<le> arctan x"
hoelzl@31098
   486
    unfolding get_even_def if_not_P[OF False] unfolding `n = Suc n'` using arctan_0_1_bounds'[OF `0 \<le> real x` `real x \<le> 1` `even (Suc (Suc n'))`] by auto
hoelzl@29805
   487
  ultimately show ?thesis by auto
hoelzl@29805
   488
qed
hoelzl@29805
   489
hoelzl@29805
   490
subsection "Compute \<pi>"
hoelzl@29805
   491
hoelzl@29805
   492
definition ub_pi :: "nat \<Rightarrow> float" where
hoelzl@31809
   493
  "ub_pi prec = (let A = rapprox_rat prec 1 5 ;
hoelzl@29805
   494
                     B = lapprox_rat prec 1 239
hoelzl@31809
   495
                 in ((Float 1 2) * ((Float 1 2) * A * (ub_arctan_horner prec (get_odd (prec div 4 + 1)) 1 (A * A)) -
hoelzl@29805
   496
                                                  B * (lb_arctan_horner prec (get_even (prec div 14 + 1)) 1 (B * B)))))"
hoelzl@29805
   497
hoelzl@29805
   498
definition lb_pi :: "nat \<Rightarrow> float" where
hoelzl@31809
   499
  "lb_pi prec = (let A = lapprox_rat prec 1 5 ;
hoelzl@29805
   500
                     B = rapprox_rat prec 1 239
hoelzl@31809
   501
                 in ((Float 1 2) * ((Float 1 2) * A * (lb_arctan_horner prec (get_even (prec div 4 + 1)) 1 (A * A)) -
hoelzl@29805
   502
                                                  B * (ub_arctan_horner prec (get_odd (prec div 14 + 1)) 1 (B * B)))))"
hoelzl@29805
   503
hoelzl@40881
   504
lemma pi_boundaries: "pi \<in> {(lb_pi n) .. (ub_pi n)}"
hoelzl@29805
   505
proof -
hoelzl@29805
   506
  have machin_pi: "pi = 4 * (4 * arctan (1 / 5) - arctan (1 / 239))" unfolding machin[symmetric] by auto
hoelzl@29805
   507
hoelzl@29805
   508
  { fix prec n :: nat fix k :: int assume "1 < k" hence "0 \<le> k" and "0 < k" and "1 \<le> k" by auto
hoelzl@29805
   509
    let ?k = "rapprox_rat prec 1 k"
hoelzl@29805
   510
    have "1 div k = 0" using div_pos_pos_trivial[OF _ `1 < k`] by auto
hoelzl@31809
   511
hoelzl@31098
   512
    have "0 \<le> real ?k" by (rule order_trans[OF _ rapprox_rat], auto simp add: `0 \<le> k`)
hoelzl@31098
   513
    have "real ?k \<le> 1" unfolding rapprox_rat.simps(2)[OF zero_le_one `0 < k`]
hoelzl@29805
   514
      by (rule rapprox_posrat_le1, auto simp add: `0 < k` `1 \<le> k`)
hoelzl@29805
   515
hoelzl@40881
   516
    have "1 / k \<le> ?k" using rapprox_rat[where x=1 and y=k] by auto
hoelzl@40881
   517
    hence "arctan (1 / k) \<le> arctan ?k" by (rule arctan_monotone')
hoelzl@40881
   518
    also have "\<dots> \<le> (?k * ub_arctan_horner prec (get_odd n) 1 (?k * ?k))"
hoelzl@31098
   519
      using arctan_0_1_bounds[OF `0 \<le> real ?k` `real ?k \<le> 1`] by auto
hoelzl@40881
   520
    finally have "arctan (1 / k) \<le> ?k * ub_arctan_horner prec (get_odd n) 1 (?k * ?k)" .
hoelzl@29805
   521
  } note ub_arctan = this
hoelzl@29805
   522
hoelzl@29805
   523
  { fix prec n :: nat fix k :: int assume "1 < k" hence "0 \<le> k" and "0 < k" by auto
hoelzl@29805
   524
    let ?k = "lapprox_rat prec 1 k"
hoelzl@29805
   525
    have "1 div k = 0" using div_pos_pos_trivial[OF _ `1 < k`] by auto
hoelzl@40881
   526
    have "1 / k \<le> 1" using `1 < k` by auto
hoelzl@29805
   527
hoelzl@31098
   528
    have "\<And>n. 0 \<le> real ?k" using lapprox_rat_bottom[where x=1 and y=k, OF zero_le_one `0 < k`] by (auto simp add: `1 div k = 0`)
hoelzl@40881
   529
    have "\<And>n. real ?k \<le> 1" using lapprox_rat by (rule order_trans, auto simp add: `1 / k \<le> 1`)
hoelzl@40881
   530
hoelzl@40881
   531
    have "?k \<le> 1 / k" using lapprox_rat[where x=1 and y=k] by auto
hoelzl@40881
   532
hoelzl@40881
   533
    have "?k * lb_arctan_horner prec (get_even n) 1 (?k * ?k) \<le> arctan ?k"
hoelzl@31098
   534
      using arctan_0_1_bounds[OF `0 \<le> real ?k` `real ?k \<le> 1`] by auto
hoelzl@40881
   535
    also have "\<dots> \<le> arctan (1 / k)" using `?k \<le> 1 / k` by (rule arctan_monotone')
hoelzl@40881
   536
    finally have "?k * lb_arctan_horner prec (get_even n) 1 (?k * ?k) \<le> arctan (1 / k)" .
hoelzl@29805
   537
  } note lb_arctan = this
hoelzl@29805
   538
hoelzl@40881
   539
  have "pi \<le> ub_pi n"
hoelzl@31098
   540
    unfolding ub_pi_def machin_pi Let_def real_of_float_mult real_of_float_sub unfolding Float_num
hoelzl@29805
   541
    using lb_arctan[of 239] ub_arctan[of 5]
hoelzl@29805
   542
    by (auto intro!: mult_left_mono add_mono simp add: diff_minus simp del: lapprox_rat.simps rapprox_rat.simps)
hoelzl@29805
   543
  moreover
hoelzl@40881
   544
  have "lb_pi n \<le> pi"
hoelzl@31098
   545
    unfolding lb_pi_def machin_pi Let_def real_of_float_mult real_of_float_sub Float_num
hoelzl@29805
   546
    using lb_arctan[of 5] ub_arctan[of 239]
hoelzl@29805
   547
    by (auto intro!: mult_left_mono add_mono simp add: diff_minus simp del: lapprox_rat.simps rapprox_rat.simps)
hoelzl@29805
   548
  ultimately show ?thesis by auto
hoelzl@29805
   549
qed
hoelzl@29805
   550
hoelzl@29805
   551
subsection "Compute arcus tangens in the entire domain"
hoelzl@29805
   552
hoelzl@31467
   553
function lb_arctan :: "nat \<Rightarrow> float \<Rightarrow> float" and ub_arctan :: "nat \<Rightarrow> float \<Rightarrow> float" where
hoelzl@29805
   554
  "lb_arctan prec x = (let ub_horner = \<lambda> x. x * ub_arctan_horner prec (get_odd (prec div 4 + 1)) 1 (x * x) ;
hoelzl@29805
   555
                           lb_horner = \<lambda> x. x * lb_arctan_horner prec (get_even (prec div 4 + 1)) 1 (x * x)
hoelzl@29805
   556
    in (if x < 0          then - ub_arctan prec (-x) else
hoelzl@29805
   557
        if x \<le> Float 1 -1 then lb_horner x else
hoelzl@31467
   558
        if x \<le> Float 1 1  then Float 1 1 * lb_horner (float_divl prec x (1 + ub_sqrt prec (1 + x * x)))
hoelzl@31467
   559
                          else (let inv = float_divr prec 1 x
hoelzl@31467
   560
                                in if inv > 1 then 0
hoelzl@29805
   561
                                              else lb_pi prec * Float 1 -1 - ub_horner inv)))"
hoelzl@29805
   562
hoelzl@29805
   563
| "ub_arctan prec x = (let lb_horner = \<lambda> x. x * lb_arctan_horner prec (get_even (prec div 4 + 1)) 1 (x * x) ;
hoelzl@29805
   564
                           ub_horner = \<lambda> x. x * ub_arctan_horner prec (get_odd (prec div 4 + 1)) 1 (x * x)
hoelzl@29805
   565
    in (if x < 0          then - lb_arctan prec (-x) else
hoelzl@29805
   566
        if x \<le> Float 1 -1 then ub_horner x else
hoelzl@31467
   567
        if x \<le> Float 1 1  then let y = float_divr prec x (1 + lb_sqrt prec (1 + x * x))
hoelzl@31467
   568
                               in if y > 1 then ub_pi prec * Float 1 -1
hoelzl@31467
   569
                                           else Float 1 1 * ub_horner y
hoelzl@29805
   570
                          else ub_pi prec * Float 1 -1 - lb_horner (float_divl prec 1 x)))"
hoelzl@29805
   571
by pat_completeness auto
hoelzl@29805
   572
termination by (relation "measure (\<lambda> v. let (prec, x) = sum_case id id v in (if x < 0 then 1 else 0))", auto simp add: less_float_def)
hoelzl@29805
   573
hoelzl@29805
   574
declare ub_arctan_horner.simps[simp del]
hoelzl@29805
   575
declare lb_arctan_horner.simps[simp del]
hoelzl@29805
   576
hoelzl@31098
   577
lemma lb_arctan_bound': assumes "0 \<le> real x"
hoelzl@40881
   578
  shows "lb_arctan prec x \<le> arctan x"
hoelzl@29805
   579
proof -
hoelzl@31098
   580
  have "\<not> x < 0" and "0 \<le> x" unfolding less_float_def le_float_def using `0 \<le> real x` by auto
hoelzl@29805
   581
  let "?ub_horner x" = "x * ub_arctan_horner prec (get_odd (prec div 4 + 1)) 1 (x * x)"
hoelzl@29805
   582
    and "?lb_horner x" = "x * lb_arctan_horner prec (get_even (prec div 4 + 1)) 1 (x * x)"
hoelzl@29805
   583
hoelzl@29805
   584
  show ?thesis
hoelzl@29805
   585
  proof (cases "x \<le> Float 1 -1")
hoelzl@31098
   586
    case True hence "real x \<le> 1" unfolding le_float_def Float_num by auto
hoelzl@29805
   587
    show ?thesis unfolding lb_arctan.simps Let_def if_not_P[OF `\<not> x < 0`] if_P[OF True]
hoelzl@31098
   588
      using arctan_0_1_bounds[OF `0 \<le> real x` `real x \<le> 1`] by auto
hoelzl@29805
   589
  next
hoelzl@31098
   590
    case False hence "0 < real x" unfolding le_float_def Float_num by auto
hoelzl@31098
   591
    let ?R = "1 + sqrt (1 + real x * real x)"
hoelzl@31467
   592
    let ?fR = "1 + ub_sqrt prec (1 + x * x)"
hoelzl@29805
   593
    let ?DIV = "float_divl prec x ?fR"
hoelzl@31467
   594
hoelzl@31098
   595
    have sqr_ge0: "0 \<le> 1 + real x * real x" using sum_power2_ge_zero[of 1 "real x", unfolded numeral_2_eq_2] by auto
hoelzl@29805
   596
    hence divisor_gt0: "0 < ?R" by (auto intro: add_pos_nonneg)
hoelzl@29805
   597
hoelzl@40881
   598
    have "sqrt (1 + x * x) \<le> ub_sqrt prec (1 + x * x)"
hoelzl@31467
   599
      using bnds_sqrt'[of "1 + x * x"] by auto
hoelzl@31467
   600
hoelzl@40881
   601
    hence "?R \<le> ?fR" by auto
hoelzl@31098
   602
    hence "0 < ?fR" and "0 < real ?fR" unfolding less_float_def using `0 < ?R` by auto
hoelzl@29805
   603
hoelzl@40881
   604
    have monotone: "(float_divl prec x ?fR) \<le> x / ?R"
hoelzl@29805
   605
    proof -
hoelzl@40881
   606
      have "?DIV \<le> real x / ?fR" by (rule float_divl)
hoelzl@40881
   607
      also have "\<dots> \<le> x / ?R" by (rule divide_left_mono[OF `?R \<le> ?fR` `0 \<le> real x` mult_pos_pos[OF order_less_le_trans[OF divisor_gt0 `?R \<le> real ?fR`] divisor_gt0]])
hoelzl@29805
   608
      finally show ?thesis .
hoelzl@29805
   609
    qed
hoelzl@29805
   610
hoelzl@29805
   611
    show ?thesis
hoelzl@29805
   612
    proof (cases "x \<le> Float 1 1")
hoelzl@29805
   613
      case True
hoelzl@31467
   614
hoelzl@40881
   615
      have "x \<le> sqrt (1 + x * x)" using real_sqrt_sum_squares_ge2[where x=1, unfolded numeral_2_eq_2] by auto
hoelzl@40881
   616
      also have "\<dots> \<le> (ub_sqrt prec (1 + x * x))"
wenzelm@32960
   617
        using bnds_sqrt'[of "1 + x * x"] by auto
hoelzl@40881
   618
      finally have "real x \<le> ?fR" by auto
hoelzl@40881
   619
      moreover have "?DIV \<le> real x / ?fR" by (rule float_divl)
hoelzl@31098
   620
      ultimately have "real ?DIV \<le> 1" unfolding divide_le_eq_1_pos[OF `0 < real ?fR`, symmetric] by auto
hoelzl@29805
   621
hoelzl@31098
   622
      have "0 \<le> real ?DIV" using float_divl_lower_bound[OF `0 \<le> x` `0 < ?fR`] unfolding le_float_def by auto
hoelzl@29805
   623
hoelzl@40881
   624
      have "(Float 1 1 * ?lb_horner ?DIV) \<le> 2 * arctan (float_divl prec x ?fR)" unfolding real_of_float_mult[of "Float 1 1"] Float_num
wenzelm@32960
   625
        using arctan_0_1_bounds[OF `0 \<le> real ?DIV` `real ?DIV \<le> 1`] by auto
hoelzl@40881
   626
      also have "\<dots> \<le> 2 * arctan (x / ?R)"
wenzelm@32960
   627
        using arctan_monotone'[OF monotone] by (auto intro!: mult_left_mono)
hoelzl@40881
   628
      also have "2 * arctan (x / ?R) = arctan x" using arctan_half[symmetric] unfolding numeral_2_eq_2 power_Suc2 power_0 mult_1_left .
hoelzl@29805
   629
      finally show ?thesis unfolding lb_arctan.simps Let_def if_not_P[OF `\<not> x < 0`] if_not_P[OF `\<not> x \<le> Float 1 -1`] if_P[OF True] .
hoelzl@29805
   630
    next
hoelzl@29805
   631
      case False
hoelzl@31098
   632
      hence "2 < real x" unfolding le_float_def Float_num by auto
hoelzl@31098
   633
      hence "1 \<le> real x" by auto
hoelzl@29805
   634
hoelzl@29805
   635
      let "?invx" = "float_divr prec 1 x"
hoelzl@40881
   636
      have "0 \<le> arctan x" using arctan_monotone'[OF `0 \<le> real x`] using arctan_tan[of 0, unfolded tan_zero] by auto
hoelzl@29805
   637
hoelzl@29805
   638
      show ?thesis
hoelzl@29805
   639
      proof (cases "1 < ?invx")
wenzelm@32960
   640
        case True
wenzelm@32960
   641
        show ?thesis unfolding lb_arctan.simps Let_def if_not_P[OF `\<not> x < 0`] if_not_P[OF `\<not> x \<le> Float 1 -1`] if_not_P[OF False] if_P[OF True]
hoelzl@40881
   642
          using `0 \<le> arctan x` by auto
hoelzl@29805
   643
      next
wenzelm@32960
   644
        case False
wenzelm@32960
   645
        hence "real ?invx \<le> 1" unfolding less_float_def by auto
wenzelm@32960
   646
        have "0 \<le> real ?invx" by (rule order_trans[OF _ float_divr], auto simp add: `0 \<le> real x`)
wenzelm@32960
   647
hoelzl@40881
   648
        have "1 / x \<noteq> 0" and "0 < 1 / x" using `0 < real x` by auto
hoelzl@40881
   649
hoelzl@40881
   650
        have "arctan (1 / x) \<le> arctan ?invx" unfolding real_of_float_1[symmetric] by (rule arctan_monotone', rule float_divr)
hoelzl@40881
   651
        also have "\<dots> \<le> (?ub_horner ?invx)" using arctan_0_1_bounds[OF `0 \<le> real ?invx` `real ?invx \<le> 1`] by auto
hoelzl@40881
   652
        finally have "pi / 2 - (?ub_horner ?invx) \<le> arctan x"
hoelzl@40881
   653
          using `0 \<le> arctan x` arctan_inverse[OF `1 / x \<noteq> 0`]
wenzelm@32960
   654
          unfolding real_sgn_pos[OF `0 < 1 / real x`] le_diff_eq by auto
wenzelm@32960
   655
        moreover
hoelzl@40881
   656
        have "lb_pi prec * Float 1 -1 \<le> pi / 2" unfolding real_of_float_mult Float_num times_divide_eq_right mult_1_left using pi_boundaries by auto
wenzelm@32960
   657
        ultimately
wenzelm@32960
   658
        show ?thesis unfolding lb_arctan.simps Let_def if_not_P[OF `\<not> x < 0`] if_not_P[OF `\<not> x \<le> Float 1 -1`] if_not_P[OF `\<not> x \<le> Float 1 1`] if_not_P[OF False]
wenzelm@32960
   659
          by auto
hoelzl@29805
   660
      qed
hoelzl@29805
   661
    qed
hoelzl@29805
   662
  qed
hoelzl@29805
   663
qed
hoelzl@29805
   664
hoelzl@31098
   665
lemma ub_arctan_bound': assumes "0 \<le> real x"
hoelzl@40881
   666
  shows "arctan x \<le> ub_arctan prec x"
hoelzl@29805
   667
proof -
hoelzl@31098
   668
  have "\<not> x < 0" and "0 \<le> x" unfolding less_float_def le_float_def using `0 \<le> real x` by auto
hoelzl@29805
   669
hoelzl@29805
   670
  let "?ub_horner x" = "x * ub_arctan_horner prec (get_odd (prec div 4 + 1)) 1 (x * x)"
hoelzl@29805
   671
    and "?lb_horner x" = "x * lb_arctan_horner prec (get_even (prec div 4 + 1)) 1 (x * x)"
hoelzl@29805
   672
hoelzl@29805
   673
  show ?thesis
hoelzl@29805
   674
  proof (cases "x \<le> Float 1 -1")
hoelzl@31098
   675
    case True hence "real x \<le> 1" unfolding le_float_def Float_num by auto
hoelzl@29805
   676
    show ?thesis unfolding ub_arctan.simps Let_def if_not_P[OF `\<not> x < 0`] if_P[OF True]
hoelzl@31098
   677
      using arctan_0_1_bounds[OF `0 \<le> real x` `real x \<le> 1`] by auto
hoelzl@29805
   678
  next
hoelzl@31098
   679
    case False hence "0 < real x" unfolding le_float_def Float_num by auto
hoelzl@31098
   680
    let ?R = "1 + sqrt (1 + real x * real x)"
hoelzl@31467
   681
    let ?fR = "1 + lb_sqrt prec (1 + x * x)"
hoelzl@29805
   682
    let ?DIV = "float_divr prec x ?fR"
hoelzl@31467
   683
hoelzl@31098
   684
    have sqr_ge0: "0 \<le> 1 + real x * real x" using sum_power2_ge_zero[of 1 "real x", unfolded numeral_2_eq_2] by auto
hoelzl@31098
   685
    hence "0 \<le> real (1 + x*x)" by auto
hoelzl@31467
   686
hoelzl@29805
   687
    hence divisor_gt0: "0 < ?R" by (auto intro: add_pos_nonneg)
hoelzl@29805
   688
hoelzl@40881
   689
    have "lb_sqrt prec (1 + x * x) \<le> sqrt (1 + x * x)"
hoelzl@31467
   690
      using bnds_sqrt'[of "1 + x * x"] by auto
hoelzl@40881
   691
    hence "?fR \<le> ?R" by auto
hoelzl@31098
   692
    have "0 < real ?fR" unfolding real_of_float_add real_of_float_1 by (rule order_less_le_trans[OF zero_less_one], auto simp add: lb_sqrt_lower_bound[OF `0 \<le> real (1 + x*x)`])
hoelzl@29805
   693
hoelzl@40881
   694
    have monotone: "x / ?R \<le> (float_divr prec x ?fR)"
hoelzl@29805
   695
    proof -
hoelzl@40881
   696
      from divide_left_mono[OF `?fR \<le> ?R` `0 \<le> real x` mult_pos_pos[OF divisor_gt0 `0 < real ?fR`]]
hoelzl@40881
   697
      have "x / ?R \<le> x / ?fR" .
hoelzl@40881
   698
      also have "\<dots> \<le> ?DIV" by (rule float_divr)
hoelzl@29805
   699
      finally show ?thesis .
hoelzl@29805
   700
    qed
hoelzl@29805
   701
hoelzl@29805
   702
    show ?thesis
hoelzl@29805
   703
    proof (cases "x \<le> Float 1 1")
hoelzl@29805
   704
      case True
hoelzl@29805
   705
      show ?thesis
hoelzl@29805
   706
      proof (cases "?DIV > 1")
wenzelm@32960
   707
        case True
hoelzl@40881
   708
        have "pi / 2 \<le> ub_pi prec * Float 1 -1" unfolding real_of_float_mult Float_num times_divide_eq_right mult_1_left using pi_boundaries by auto
wenzelm@32960
   709
        from order_less_le_trans[OF arctan_ubound this, THEN less_imp_le]
wenzelm@32960
   710
        show ?thesis unfolding ub_arctan.simps Let_def if_not_P[OF `\<not> x < 0`] if_not_P[OF `\<not> x \<le> Float 1 -1`] if_P[OF `x \<le> Float 1 1`] if_P[OF True] .
hoelzl@29805
   711
      next
wenzelm@32960
   712
        case False
wenzelm@32960
   713
        hence "real ?DIV \<le> 1" unfolding less_float_def by auto
wenzelm@32960
   714
huffman@44349
   715
        have "0 \<le> x / ?R" using `0 \<le> real x` `0 < ?R` unfolding zero_le_divide_iff by auto
wenzelm@32960
   716
        hence "0 \<le> real ?DIV" using monotone by (rule order_trans)
wenzelm@32960
   717
hoelzl@40881
   718
        have "arctan x = 2 * arctan (x / ?R)" using arctan_half unfolding numeral_2_eq_2 power_Suc2 power_0 mult_1_left .
hoelzl@40881
   719
        also have "\<dots> \<le> 2 * arctan (?DIV)"
wenzelm@32960
   720
          using arctan_monotone'[OF monotone] by (auto intro!: mult_left_mono)
hoelzl@40881
   721
        also have "\<dots> \<le> (Float 1 1 * ?ub_horner ?DIV)" unfolding real_of_float_mult[of "Float 1 1"] Float_num
wenzelm@32960
   722
          using arctan_0_1_bounds[OF `0 \<le> real ?DIV` `real ?DIV \<le> 1`] by auto
wenzelm@32960
   723
        finally show ?thesis unfolding ub_arctan.simps Let_def if_not_P[OF `\<not> x < 0`] if_not_P[OF `\<not> x \<le> Float 1 -1`] if_P[OF `x \<le> Float 1 1`] if_not_P[OF False] .
hoelzl@29805
   724
      qed
hoelzl@29805
   725
    next
hoelzl@29805
   726
      case False
hoelzl@31098
   727
      hence "2 < real x" unfolding le_float_def Float_num by auto
hoelzl@31098
   728
      hence "1 \<le> real x" by auto
hoelzl@31098
   729
      hence "0 < real x" by auto
hoelzl@29805
   730
      hence "0 < x" unfolding less_float_def by auto
hoelzl@29805
   731
hoelzl@29805
   732
      let "?invx" = "float_divl prec 1 x"
hoelzl@40881
   733
      have "0 \<le> arctan x" using arctan_monotone'[OF `0 \<le> real x`] using arctan_tan[of 0, unfolded tan_zero] by auto
hoelzl@29805
   734
hoelzl@31098
   735
      have "real ?invx \<le> 1" unfolding less_float_def by (rule order_trans[OF float_divl], auto simp add: `1 \<le> real x` divide_le_eq_1_pos[OF `0 < real x`])
hoelzl@31098
   736
      have "0 \<le> real ?invx" unfolding real_of_float_0[symmetric] by (rule float_divl_lower_bound[unfolded le_float_def], auto simp add: `0 < x`)
hoelzl@31467
   737
hoelzl@40881
   738
      have "1 / x \<noteq> 0" and "0 < 1 / x" using `0 < real x` by auto
hoelzl@40881
   739
hoelzl@40881
   740
      have "(?lb_horner ?invx) \<le> arctan (?invx)" using arctan_0_1_bounds[OF `0 \<le> real ?invx` `real ?invx \<le> 1`] by auto
hoelzl@40881
   741
      also have "\<dots> \<le> arctan (1 / x)" unfolding real_of_float_1[symmetric] by (rule arctan_monotone', rule float_divl)
hoelzl@40881
   742
      finally have "arctan x \<le> pi / 2 - (?lb_horner ?invx)"
hoelzl@40881
   743
        using `0 \<le> arctan x` arctan_inverse[OF `1 / x \<noteq> 0`]
hoelzl@40881
   744
        unfolding real_sgn_pos[OF `0 < 1 / x`] le_diff_eq by auto
hoelzl@29805
   745
      moreover
hoelzl@40881
   746
      have "pi / 2 \<le> ub_pi prec * Float 1 -1" unfolding real_of_float_mult Float_num times_divide_eq_right mult_1_right using pi_boundaries by auto
hoelzl@29805
   747
      ultimately
hoelzl@29805
   748
      show ?thesis unfolding ub_arctan.simps Let_def if_not_P[OF `\<not> x < 0`] if_not_P[OF `\<not> x \<le> Float 1 -1`] if_not_P[OF `\<not> x \<le> Float 1 1`] if_not_P[OF False]
wenzelm@32960
   749
        by auto
hoelzl@29805
   750
    qed
hoelzl@29805
   751
  qed
hoelzl@29805
   752
qed
hoelzl@29805
   753
hoelzl@29805
   754
lemma arctan_boundaries:
hoelzl@40881
   755
  "arctan x \<in> {(lb_arctan prec x) .. (ub_arctan prec x)}"
hoelzl@29805
   756
proof (cases "0 \<le> x")
hoelzl@31098
   757
  case True hence "0 \<le> real x" unfolding le_float_def by auto
hoelzl@31098
   758
  show ?thesis using ub_arctan_bound'[OF `0 \<le> real x`] lb_arctan_bound'[OF `0 \<le> real x`] unfolding atLeastAtMost_iff by auto
hoelzl@29805
   759
next
hoelzl@29805
   760
  let ?mx = "-x"
hoelzl@31098
   761
  case False hence "x < 0" and "0 \<le> real ?mx" unfolding le_float_def less_float_def by auto
hoelzl@40881
   762
  hence bounds: "lb_arctan prec ?mx \<le> arctan ?mx \<and> arctan ?mx \<le> ub_arctan prec ?mx"
hoelzl@31098
   763
    using ub_arctan_bound'[OF `0 \<le> real ?mx`] lb_arctan_bound'[OF `0 \<le> real ?mx`] by auto
hoelzl@31098
   764
  show ?thesis unfolding real_of_float_minus arctan_minus lb_arctan.simps[where x=x] ub_arctan.simps[where x=x] Let_def if_P[OF `x < 0`]
hoelzl@31098
   765
    unfolding atLeastAtMost_iff using bounds[unfolded real_of_float_minus arctan_minus] by auto
hoelzl@29805
   766
qed
hoelzl@29805
   767
hoelzl@40881
   768
lemma bnds_arctan: "\<forall> (x::real) lx ux. (l, u) = (lb_arctan prec lx, ub_arctan prec ux) \<and> x \<in> {lx .. ux} \<longrightarrow> l \<le> arctan x \<and> arctan x \<le> u"
hoelzl@29805
   769
proof (rule allI, rule allI, rule allI, rule impI)
hoelzl@40881
   770
  fix x :: real fix lx ux
hoelzl@40881
   771
  assume "(l, u) = (lb_arctan prec lx, ub_arctan prec ux) \<and> x \<in> {lx .. ux}"
hoelzl@40881
   772
  hence l: "lb_arctan prec lx = l " and u: "ub_arctan prec ux = u" and x: "x \<in> {lx .. ux}" by auto
hoelzl@29805
   773
hoelzl@29805
   774
  { from arctan_boundaries[of lx prec, unfolded l]
hoelzl@40881
   775
    have "l \<le> arctan lx" by (auto simp del: lb_arctan.simps)
hoelzl@29805
   776
    also have "\<dots> \<le> arctan x" using x by (auto intro: arctan_monotone')
hoelzl@40881
   777
    finally have "l \<le> arctan x" .
hoelzl@29805
   778
  } moreover
hoelzl@40881
   779
  { have "arctan x \<le> arctan ux" using x by (auto intro: arctan_monotone')
hoelzl@40881
   780
    also have "\<dots> \<le> u" using arctan_boundaries[of ux prec, unfolded u] by (auto simp del: ub_arctan.simps)
hoelzl@40881
   781
    finally have "arctan x \<le> u" .
hoelzl@40881
   782
  } ultimately show "l \<le> arctan x \<and> arctan x \<le> u" ..
hoelzl@29805
   783
qed
hoelzl@29805
   784
hoelzl@29805
   785
section "Sinus and Cosinus"
hoelzl@29805
   786
hoelzl@29805
   787
subsection "Compute the cosinus and sinus series"
hoelzl@29805
   788
hoelzl@29805
   789
fun ub_sin_cos_aux :: "nat \<Rightarrow> nat \<Rightarrow> nat \<Rightarrow> nat \<Rightarrow> float \<Rightarrow> float"
hoelzl@29805
   790
and lb_sin_cos_aux :: "nat \<Rightarrow> nat \<Rightarrow> nat \<Rightarrow> nat \<Rightarrow> float \<Rightarrow> float" where
hoelzl@29805
   791
  "ub_sin_cos_aux prec 0 i k x = 0"
hoelzl@31809
   792
| "ub_sin_cos_aux prec (Suc n) i k x =
hoelzl@40881
   793
    (rapprox_rat prec 1 k) - x * (lb_sin_cos_aux prec n (i + 2) (k * i * (i + 1)) x)"
hoelzl@29805
   794
| "lb_sin_cos_aux prec 0 i k x = 0"
hoelzl@31809
   795
| "lb_sin_cos_aux prec (Suc n) i k x =
hoelzl@40881
   796
    (lapprox_rat prec 1 k) - x * (ub_sin_cos_aux prec n (i + 2) (k * i * (i + 1)) x)"
hoelzl@29805
   797
lemma cos_aux:
hoelzl@40881
   798
  shows "(lb_sin_cos_aux prec n 1 1 (x * x)) \<le> (\<Sum> i=0..<n. -1^i * (1/real (fact (2 * i))) * x ^(2 * i))" (is "?lb")
hoelzl@40881
   799
  and "(\<Sum> i=0..<n. -1^i * (1/real (fact (2 * i))) * x^(2 * i)) \<le> (ub_sin_cos_aux prec n 1 1 (x * x))" (is "?ub")
hoelzl@29805
   800
proof -
hoelzl@31098
   801
  have "0 \<le> real (x * x)" unfolding real_of_float_mult by auto
hoelzl@29805
   802
  let "?f n" = "fact (2 * n)"
hoelzl@29805
   803
hoelzl@31809
   804
  { fix n
haftmann@30971
   805
    have F: "\<And>m. ((\<lambda>i. i + 2) ^^ n) m = m + 2 * n" by (induct n arbitrary: m, auto)
haftmann@30971
   806
    have "?f (Suc n) = ?f n * ((\<lambda>i. i + 2) ^^ n) 1 * (((\<lambda>i. i + 2) ^^ n) 1 + 1)"
hoelzl@29805
   807
      unfolding F by auto } note f_eq = this
hoelzl@31809
   808
hoelzl@31809
   809
  from horner_bounds[where lb="lb_sin_cos_aux prec" and ub="ub_sin_cos_aux prec" and j'=0,
hoelzl@31098
   810
    OF `0 \<le> real (x * x)` f_eq lb_sin_cos_aux.simps ub_sin_cos_aux.simps]
hoelzl@31098
   811
  show "?lb" and "?ub" by (auto simp add: power_mult power2_eq_square[of "real x"])
hoelzl@29805
   812
qed
hoelzl@29805
   813
hoelzl@40881
   814
lemma cos_boundaries: assumes "0 \<le> real x" and "x \<le> pi / 2"
hoelzl@40881
   815
  shows "cos x \<in> {(lb_sin_cos_aux prec (get_even n) 1 1 (x * x)) .. (ub_sin_cos_aux prec (get_odd n) 1 1 (x * x))}"
hoelzl@31098
   816
proof (cases "real x = 0")
hoelzl@31098
   817
  case False hence "real x \<noteq> 0" by auto
hoelzl@31098
   818
  hence "0 < x" and "0 < real x" using `0 \<le> real x` unfolding less_float_def by auto
hoelzl@31098
   819
  have "0 < x * x" using `0 < x` unfolding less_float_def real_of_float_mult real_of_float_0
hoelzl@31098
   820
    using mult_pos_pos[where a="real x" and b="real x"] by auto
hoelzl@29805
   821
haftmann@30952
   822
  { fix x n have "(\<Sum> i=0..<n. -1^i * (1/real (fact (2 * i))) * x ^ (2 * i))
hoelzl@29805
   823
    = (\<Sum> i = 0 ..< 2 * n. (if even(i) then (-1 ^ (i div 2))/(real (fact i)) else 0) * x ^ i)" (is "?sum = ?ifsum")
hoelzl@29805
   824
  proof -
hoelzl@29805
   825
    have "?sum = ?sum + (\<Sum> j = 0 ..< n. 0)" by auto
hoelzl@31809
   826
    also have "\<dots> =
hoelzl@29805
   827
      (\<Sum> j = 0 ..< n. -1 ^ ((2 * j) div 2) / (real (fact (2 * j))) * x ^(2 * j)) + (\<Sum> j = 0 ..< n. 0)" by auto
hoelzl@29805
   828
    also have "\<dots> = (\<Sum> i = 0 ..< 2 * n. if even i then -1 ^ (i div 2) / (real (fact i)) * x ^ i else 0)"
hoelzl@29805
   829
      unfolding sum_split_even_odd ..
hoelzl@29805
   830
    also have "\<dots> = (\<Sum> i = 0 ..< 2 * n. (if even i then -1 ^ (i div 2) / (real (fact i)) else 0) * x ^ i)"
hoelzl@29805
   831
      by (rule setsum_cong2) auto
hoelzl@29805
   832
    finally show ?thesis by assumption
hoelzl@29805
   833
  qed } note morph_to_if_power = this
hoelzl@29805
   834
hoelzl@29805
   835
hoelzl@29805
   836
  { fix n :: nat assume "0 < n"
hoelzl@29805
   837
    hence "0 < 2 * n" by auto
hoelzl@31098
   838
    obtain t where "0 < t" and "t < real x" and
hoelzl@40881
   839
      cos_eq: "cos x = (\<Sum> i = 0 ..< 2 * n. (if even(i) then (-1 ^ (i div 2))/(real (fact i)) else 0) * (real x) ^ i)
hoelzl@40881
   840
      + (cos (t + 1/2 * (2 * n) * pi) / real (fact (2*n))) * (real x)^(2*n)"
hoelzl@29805
   841
      (is "_ = ?SUM + ?rest / ?fact * ?pow")
huffman@44306
   842
      using Maclaurin_cos_expansion2[OF `0 < real x` `0 < 2 * n`]
huffman@44306
   843
      unfolding cos_coeff_def by auto
hoelzl@29805
   844
hoelzl@40881
   845
    have "cos t * -1^n = cos t * cos (n * pi) + sin t * sin (n * pi)" by auto
hoelzl@40881
   846
    also have "\<dots> = cos (t + n * pi)"  using cos_add by auto
hoelzl@29805
   847
    also have "\<dots> = ?rest" by auto
hoelzl@29805
   848
    finally have "cos t * -1^n = ?rest" .
hoelzl@29805
   849
    moreover
hoelzl@40881
   850
    have "t \<le> pi / 2" using `t < real x` and `x \<le> pi / 2` by auto
hoelzl@29805
   851
    hence "0 \<le> cos t" using `0 < t` and cos_ge_zero by auto
hoelzl@29805
   852
    ultimately have even: "even n \<Longrightarrow> 0 \<le> ?rest" and odd: "odd n \<Longrightarrow> 0 \<le> - ?rest " by auto
hoelzl@29805
   853
hoelzl@29805
   854
    have "0 < ?fact" by auto
hoelzl@31098
   855
    have "0 < ?pow" using `0 < real x` by auto
hoelzl@29805
   856
hoelzl@29805
   857
    {
hoelzl@29805
   858
      assume "even n"
hoelzl@40881
   859
      have "(lb_sin_cos_aux prec n 1 1 (x * x)) \<le> ?SUM"
wenzelm@32960
   860
        unfolding morph_to_if_power[symmetric] using cos_aux by auto
hoelzl@40881
   861
      also have "\<dots> \<le> cos x"
hoelzl@29805
   862
      proof -
wenzelm@32960
   863
        from even[OF `even n`] `0 < ?fact` `0 < ?pow`
wenzelm@32960
   864
        have "0 \<le> (?rest / ?fact) * ?pow" by (metis mult_nonneg_nonneg divide_nonneg_pos less_imp_le)
wenzelm@32960
   865
        thus ?thesis unfolding cos_eq by auto
hoelzl@29805
   866
      qed
hoelzl@40881
   867
      finally have "(lb_sin_cos_aux prec n 1 1 (x * x)) \<le> cos x" .
hoelzl@29805
   868
    } note lb = this
hoelzl@29805
   869
hoelzl@29805
   870
    {
hoelzl@29805
   871
      assume "odd n"
hoelzl@40881
   872
      have "cos x \<le> ?SUM"
hoelzl@29805
   873
      proof -
wenzelm@32960
   874
        from `0 < ?fact` and `0 < ?pow` and odd[OF `odd n`]
wenzelm@32960
   875
        have "0 \<le> (- ?rest) / ?fact * ?pow"
wenzelm@32960
   876
          by (metis mult_nonneg_nonneg divide_nonneg_pos less_imp_le)
wenzelm@32960
   877
        thus ?thesis unfolding cos_eq by auto
hoelzl@29805
   878
      qed
hoelzl@40881
   879
      also have "\<dots> \<le> (ub_sin_cos_aux prec n 1 1 (x * x))"
wenzelm@32960
   880
        unfolding morph_to_if_power[symmetric] using cos_aux by auto
hoelzl@40881
   881
      finally have "cos x \<le> (ub_sin_cos_aux prec n 1 1 (x * x))" .
hoelzl@29805
   882
    } note ub = this and lb
hoelzl@29805
   883
  } note ub = this(1) and lb = this(2)
hoelzl@29805
   884
hoelzl@40881
   885
  have "cos x \<le> (ub_sin_cos_aux prec (get_odd n) 1 1 (x * x))" using ub[OF odd_pos[OF get_odd] get_odd] .
hoelzl@40881
   886
  moreover have "(lb_sin_cos_aux prec (get_even n) 1 1 (x * x)) \<le> cos x"
hoelzl@29805
   887
  proof (cases "0 < get_even n")
hoelzl@29805
   888
    case True show ?thesis using lb[OF True get_even] .
hoelzl@29805
   889
  next
hoelzl@29805
   890
    case False
hoelzl@29805
   891
    hence "get_even n = 0" by auto
hoelzl@40881
   892
    have "- (pi / 2) \<le> x" by (rule order_trans[OF _ `0 < real x`[THEN less_imp_le]], auto)
hoelzl@40881
   893
    with `x \<le> pi / 2`
hoelzl@31098
   894
    show ?thesis unfolding `get_even n = 0` lb_sin_cos_aux.simps real_of_float_minus real_of_float_0 using cos_ge_zero by auto
hoelzl@29805
   895
  qed
hoelzl@29805
   896
  ultimately show ?thesis by auto
hoelzl@29805
   897
next
hoelzl@29805
   898
  case True
hoelzl@29805
   899
  show ?thesis
hoelzl@29805
   900
  proof (cases "n = 0")
hoelzl@31809
   901
    case True
hoelzl@31098
   902
    thus ?thesis unfolding `n = 0` get_even_def get_odd_def using `real x = 0` lapprox_rat[where x="-1" and y=1] by auto
hoelzl@29805
   903
  next
hoelzl@29805
   904
    case False with not0_implies_Suc obtain m where "n = Suc m" by blast
hoelzl@31098
   905
    thus ?thesis unfolding `n = Suc m` get_even_def get_odd_def using `real x = 0` rapprox_rat[where x=1 and y=1] lapprox_rat[where x=1 and y=1] by (cases "even (Suc m)", auto)
hoelzl@29805
   906
  qed
hoelzl@29805
   907
qed
hoelzl@29805
   908
hoelzl@31098
   909
lemma sin_aux: assumes "0 \<le> real x"
hoelzl@40881
   910
  shows "(x * lb_sin_cos_aux prec n 2 1 (x * x)) \<le> (\<Sum> i=0..<n. -1^i * (1/real (fact (2 * i + 1))) * x^(2 * i + 1))" (is "?lb")
hoelzl@40881
   911
  and "(\<Sum> i=0..<n. -1^i * (1/real (fact (2 * i + 1))) * x^(2 * i + 1)) \<le> (x * ub_sin_cos_aux prec n 2 1 (x * x))" (is "?ub")
hoelzl@29805
   912
proof -
hoelzl@31098
   913
  have "0 \<le> real (x * x)" unfolding real_of_float_mult by auto
hoelzl@29805
   914
  let "?f n" = "fact (2 * n + 1)"
hoelzl@29805
   915
hoelzl@31809
   916
  { fix n
haftmann@30971
   917
    have F: "\<And>m. ((\<lambda>i. i + 2) ^^ n) m = m + 2 * n" by (induct n arbitrary: m, auto)
haftmann@30971
   918
    have "?f (Suc n) = ?f n * ((\<lambda>i. i + 2) ^^ n) 2 * (((\<lambda>i. i + 2) ^^ n) 2 + 1)"
hoelzl@29805
   919
      unfolding F by auto } note f_eq = this
hoelzl@31809
   920
hoelzl@29805
   921
  from horner_bounds[where lb="lb_sin_cos_aux prec" and ub="ub_sin_cos_aux prec" and j'=0,
hoelzl@31098
   922
    OF `0 \<le> real (x * x)` f_eq lb_sin_cos_aux.simps ub_sin_cos_aux.simps]
hoelzl@31098
   923
  show "?lb" and "?ub" using `0 \<le> real x` unfolding real_of_float_mult
huffman@36778
   924
    unfolding power_add power_one_right mult_assoc[symmetric] setsum_left_distrib[symmetric]
huffman@36778
   925
    unfolding mult_commute[where 'a=real]
hoelzl@31098
   926
    by (auto intro!: mult_left_mono simp add: power_mult power2_eq_square[of "real x"])
hoelzl@29805
   927
qed
hoelzl@29805
   928
hoelzl@40881
   929
lemma sin_boundaries: assumes "0 \<le> real x" and "x \<le> pi / 2"
hoelzl@40881
   930
  shows "sin x \<in> {(x * lb_sin_cos_aux prec (get_even n) 2 1 (x * x)) .. (x * ub_sin_cos_aux prec (get_odd n) 2 1 (x * x))}"
hoelzl@31098
   931
proof (cases "real x = 0")
hoelzl@31098
   932
  case False hence "real x \<noteq> 0" by auto
hoelzl@31098
   933
  hence "0 < x" and "0 < real x" using `0 \<le> real x` unfolding less_float_def by auto
hoelzl@31098
   934
  have "0 < x * x" using `0 < x` unfolding less_float_def real_of_float_mult real_of_float_0
hoelzl@31098
   935
    using mult_pos_pos[where a="real x" and b="real x"] by auto
hoelzl@29805
   936
hoelzl@29805
   937
  { fix x n have "(\<Sum> j = 0 ..< n. -1 ^ (((2 * j + 1) - Suc 0) div 2) / (real (fact (2 * j + 1))) * x ^(2 * j + 1))
hoelzl@29805
   938
    = (\<Sum> i = 0 ..< 2 * n. (if even(i) then 0 else (-1 ^ ((i - Suc 0) div 2))/(real (fact i))) * x ^ i)" (is "?SUM = _")
hoelzl@29805
   939
    proof -
hoelzl@29805
   940
      have pow: "!!i. x ^ (2 * i + 1) = x * x ^ (2 * i)" by auto
hoelzl@29805
   941
      have "?SUM = (\<Sum> j = 0 ..< n. 0) + ?SUM" by auto
hoelzl@29805
   942
      also have "\<dots> = (\<Sum> i = 0 ..< 2 * n. if even i then 0 else -1 ^ ((i - Suc 0) div 2) / (real (fact i)) * x ^ i)"
wenzelm@32960
   943
        unfolding sum_split_even_odd ..
hoelzl@29805
   944
      also have "\<dots> = (\<Sum> i = 0 ..< 2 * n. (if even i then 0 else -1 ^ ((i - Suc 0) div 2) / (real (fact i))) * x ^ i)"
wenzelm@32960
   945
        by (rule setsum_cong2) auto
hoelzl@29805
   946
      finally show ?thesis by assumption
hoelzl@29805
   947
    qed } note setsum_morph = this
hoelzl@29805
   948
hoelzl@29805
   949
  { fix n :: nat assume "0 < n"
hoelzl@29805
   950
    hence "0 < 2 * n + 1" by auto
hoelzl@31098
   951
    obtain t where "0 < t" and "t < real x" and
hoelzl@40881
   952
      sin_eq: "sin x = (\<Sum> i = 0 ..< 2 * n + 1. (if even(i) then 0 else (-1 ^ ((i - Suc 0) div 2))/(real (fact i))) * (real x) ^ i)
hoelzl@40881
   953
      + (sin (t + 1/2 * (2 * n + 1) * pi) / real (fact (2*n + 1))) * (real x)^(2*n + 1)"
hoelzl@29805
   954
      (is "_ = ?SUM + ?rest / ?fact * ?pow")
huffman@44306
   955
      using Maclaurin_sin_expansion3[OF `0 < 2 * n + 1` `0 < real x`]
huffman@44306
   956
      unfolding sin_coeff_def by auto
hoelzl@29805
   957
hoelzl@29805
   958
    have "?rest = cos t * -1^n" unfolding sin_add cos_add real_of_nat_add left_distrib right_distrib by auto
hoelzl@29805
   959
    moreover
hoelzl@40881
   960
    have "t \<le> pi / 2" using `t < real x` and `x \<le> pi / 2` by auto
hoelzl@29805
   961
    hence "0 \<le> cos t" using `0 < t` and cos_ge_zero by auto
hoelzl@29805
   962
    ultimately have even: "even n \<Longrightarrow> 0 \<le> ?rest" and odd: "odd n \<Longrightarrow> 0 \<le> - ?rest " by auto
hoelzl@29805
   963
huffman@44305
   964
    have "0 < ?fact" by (simp del: fact_Suc)
hoelzl@31098
   965
    have "0 < ?pow" using `0 < real x` by (rule zero_less_power)
hoelzl@29805
   966
hoelzl@29805
   967
    {
hoelzl@29805
   968
      assume "even n"
hoelzl@40881
   969
      have "(x * lb_sin_cos_aux prec n 2 1 (x * x)) \<le>
hoelzl@31098
   970
            (\<Sum> i = 0 ..< 2 * n. (if even(i) then 0 else (-1 ^ ((i - Suc 0) div 2))/(real (fact i))) * (real x) ^ i)"
wenzelm@32960
   971
        using sin_aux[OF `0 \<le> real x`] unfolding setsum_morph[symmetric] by auto
hoelzl@29805
   972
      also have "\<dots> \<le> ?SUM" by auto
hoelzl@40881
   973
      also have "\<dots> \<le> sin x"
hoelzl@29805
   974
      proof -
wenzelm@32960
   975
        from even[OF `even n`] `0 < ?fact` `0 < ?pow`
wenzelm@32960
   976
        have "0 \<le> (?rest / ?fact) * ?pow" by (metis mult_nonneg_nonneg divide_nonneg_pos less_imp_le)
wenzelm@32960
   977
        thus ?thesis unfolding sin_eq by auto
hoelzl@29805
   978
      qed
hoelzl@40881
   979
      finally have "(x * lb_sin_cos_aux prec n 2 1 (x * x)) \<le> sin x" .
hoelzl@29805
   980
    } note lb = this
hoelzl@29805
   981
hoelzl@29805
   982
    {
hoelzl@29805
   983
      assume "odd n"
hoelzl@40881
   984
      have "sin x \<le> ?SUM"
hoelzl@29805
   985
      proof -
wenzelm@32960
   986
        from `0 < ?fact` and `0 < ?pow` and odd[OF `odd n`]
wenzelm@32960
   987
        have "0 \<le> (- ?rest) / ?fact * ?pow"
wenzelm@32960
   988
          by (metis mult_nonneg_nonneg divide_nonneg_pos less_imp_le)
wenzelm@32960
   989
        thus ?thesis unfolding sin_eq by auto
hoelzl@29805
   990
      qed
hoelzl@31098
   991
      also have "\<dots> \<le> (\<Sum> i = 0 ..< 2 * n. (if even(i) then 0 else (-1 ^ ((i - Suc 0) div 2))/(real (fact i))) * (real x) ^ i)"
wenzelm@32960
   992
         by auto
hoelzl@40881
   993
      also have "\<dots> \<le> (x * ub_sin_cos_aux prec n 2 1 (x * x))"
wenzelm@32960
   994
        using sin_aux[OF `0 \<le> real x`] unfolding setsum_morph[symmetric] by auto
hoelzl@40881
   995
      finally have "sin x \<le> (x * ub_sin_cos_aux prec n 2 1 (x * x))" .
hoelzl@29805
   996
    } note ub = this and lb
hoelzl@29805
   997
  } note ub = this(1) and lb = this(2)
hoelzl@29805
   998
hoelzl@40881
   999
  have "sin x \<le> (x * ub_sin_cos_aux prec (get_odd n) 2 1 (x * x))" using ub[OF odd_pos[OF get_odd] get_odd] .
hoelzl@40881
  1000
  moreover have "(x * lb_sin_cos_aux prec (get_even n) 2 1 (x * x)) \<le> sin x"
hoelzl@29805
  1001
  proof (cases "0 < get_even n")
hoelzl@29805
  1002
    case True show ?thesis using lb[OF True get_even] .
hoelzl@29805
  1003
  next
hoelzl@29805
  1004
    case False
hoelzl@29805
  1005
    hence "get_even n = 0" by auto
hoelzl@40881
  1006
    with `x \<le> pi / 2` `0 \<le> real x`
hoelzl@31098
  1007
    show ?thesis unfolding `get_even n = 0` ub_sin_cos_aux.simps real_of_float_minus real_of_float_0 using sin_ge_zero by auto
hoelzl@29805
  1008
  qed
hoelzl@29805
  1009
  ultimately show ?thesis by auto
hoelzl@29805
  1010
next
hoelzl@29805
  1011
  case True
hoelzl@29805
  1012
  show ?thesis
hoelzl@29805
  1013
  proof (cases "n = 0")
hoelzl@31809
  1014
    case True
hoelzl@31098
  1015
    thus ?thesis unfolding `n = 0` get_even_def get_odd_def using `real x = 0` lapprox_rat[where x="-1" and y=1] by auto
hoelzl@29805
  1016
  next
hoelzl@29805
  1017
    case False with not0_implies_Suc obtain m where "n = Suc m" by blast
hoelzl@31098
  1018
    thus ?thesis unfolding `n = Suc m` get_even_def get_odd_def using `real x = 0` rapprox_rat[where x=1 and y=1] lapprox_rat[where x=1 and y=1] by (cases "even (Suc m)", auto)
hoelzl@29805
  1019
  qed
hoelzl@29805
  1020
qed
hoelzl@29805
  1021
hoelzl@29805
  1022
subsection "Compute the cosinus in the entire domain"
hoelzl@29805
  1023
hoelzl@29805
  1024
definition lb_cos :: "nat \<Rightarrow> float \<Rightarrow> float" where
hoelzl@29805
  1025
"lb_cos prec x = (let
hoelzl@29805
  1026
    horner = \<lambda> x. lb_sin_cos_aux prec (get_even (prec div 4 + 1)) 1 1 (x * x) ;
hoelzl@29805
  1027
    half = \<lambda> x. if x < 0 then - 1 else Float 1 1 * x * x - 1
hoelzl@29805
  1028
  in if x < Float 1 -1 then horner x
hoelzl@29805
  1029
else if x < 1          then half (horner (x * Float 1 -1))
hoelzl@29805
  1030
                       else half (half (horner (x * Float 1 -2))))"
hoelzl@29805
  1031
hoelzl@29805
  1032
definition ub_cos :: "nat \<Rightarrow> float \<Rightarrow> float" where
hoelzl@29805
  1033
"ub_cos prec x = (let
hoelzl@29805
  1034
    horner = \<lambda> x. ub_sin_cos_aux prec (get_odd (prec div 4 + 1)) 1 1 (x * x) ;
hoelzl@29805
  1035
    half = \<lambda> x. Float 1 1 * x * x - 1
hoelzl@29805
  1036
  in if x < Float 1 -1 then horner x
hoelzl@29805
  1037
else if x < 1          then half (horner (x * Float 1 -1))
hoelzl@29805
  1038
                       else half (half (horner (x * Float 1 -2))))"
hoelzl@29805
  1039
hoelzl@40881
  1040
lemma lb_cos: assumes "0 \<le> real x" and "x \<le> pi"
hoelzl@40881
  1041
  shows "cos x \<in> {(lb_cos prec x) .. (ub_cos prec x)}" (is "?cos x \<in> {(?lb x) .. (?ub x) }")
hoelzl@29805
  1042
proof -
hoelzl@29805
  1043
  { fix x :: real
hoelzl@29805
  1044
    have "cos x = cos (x / 2 + x / 2)" by auto
hoelzl@29805
  1045
    also have "\<dots> = cos (x / 2) * cos (x / 2) + sin (x / 2) * sin (x / 2) - sin (x / 2) * sin (x / 2) + cos (x / 2) * cos (x / 2) - 1"
hoelzl@29805
  1046
      unfolding cos_add by auto
hoelzl@29805
  1047
    also have "\<dots> = 2 * cos (x / 2) * cos (x / 2) - 1" by algebra
hoelzl@29805
  1048
    finally have "cos x = 2 * cos (x / 2) * cos (x / 2) - 1" .
hoelzl@29805
  1049
  } note x_half = this[symmetric]
hoelzl@29805
  1050
hoelzl@31098
  1051
  have "\<not> x < 0" using `0 \<le> real x` unfolding less_float_def by auto
hoelzl@29805
  1052
  let "?ub_horner x" = "ub_sin_cos_aux prec (get_odd (prec div 4 + 1)) 1 1 (x * x)"
hoelzl@29805
  1053
  let "?lb_horner x" = "lb_sin_cos_aux prec (get_even (prec div 4 + 1)) 1 1 (x * x)"
hoelzl@29805
  1054
  let "?ub_half x" = "Float 1 1 * x * x - 1"
hoelzl@29805
  1055
  let "?lb_half x" = "if x < 0 then - 1 else Float 1 1 * x * x - 1"
hoelzl@29805
  1056
hoelzl@29805
  1057
  show ?thesis
hoelzl@29805
  1058
  proof (cases "x < Float 1 -1")
hoelzl@40881
  1059
    case True hence "x \<le> pi / 2" unfolding less_float_def using pi_ge_two by auto
hoelzl@29805
  1060
    show ?thesis unfolding lb_cos_def[where x=x] ub_cos_def[where x=x] if_not_P[OF `\<not> x < 0`] if_P[OF `x < Float 1 -1`] Let_def
hoelzl@40881
  1061
      using cos_boundaries[OF `0 \<le> real x` `x \<le> pi / 2`] .
hoelzl@29805
  1062
  next
hoelzl@29805
  1063
    case False
hoelzl@40881
  1064
    { fix y x :: float let ?x2 = "(x * Float 1 -1)"
hoelzl@40881
  1065
      assume "y \<le> cos ?x2" and "-pi \<le> x" and "x \<le> pi"
hoelzl@31098
  1066
      hence "- (pi / 2) \<le> ?x2" and "?x2 \<le> pi / 2" using pi_ge_two unfolding real_of_float_mult Float_num by auto
hoelzl@29805
  1067
      hence "0 \<le> cos ?x2" by (rule cos_ge_zero)
hoelzl@31467
  1068
hoelzl@40881
  1069
      have "(?lb_half y) \<le> cos x"
hoelzl@29805
  1070
      proof (cases "y < 0")
wenzelm@32960
  1071
        case True show ?thesis using cos_ge_minus_one unfolding if_P[OF True] by auto
hoelzl@29805
  1072
      next
wenzelm@32960
  1073
        case False
wenzelm@32960
  1074
        hence "0 \<le> real y" unfolding less_float_def by auto
hoelzl@40881
  1075
        from mult_mono[OF `y \<le> cos ?x2` `y \<le> cos ?x2` `0 \<le> cos ?x2` this]
wenzelm@32960
  1076
        have "real y * real y \<le> cos ?x2 * cos ?x2" .
wenzelm@32960
  1077
        hence "2 * real y * real y \<le> 2 * cos ?x2 * cos ?x2" by auto
hoelzl@40881
  1078
        hence "2 * real y * real y - 1 \<le> 2 * cos (x / 2) * cos (x / 2) - 1" unfolding Float_num real_of_float_mult by auto
wenzelm@32960
  1079
        thus ?thesis unfolding if_not_P[OF False] x_half Float_num real_of_float_mult real_of_float_sub by auto
hoelzl@29805
  1080
      qed
hoelzl@29805
  1081
    } note lb_half = this
hoelzl@31467
  1082
hoelzl@40881
  1083
    { fix y x :: float let ?x2 = "(x * Float 1 -1)"
hoelzl@40881
  1084
      assume ub: "cos ?x2 \<le> y" and "- pi \<le> x" and "x \<le> pi"
hoelzl@31098
  1085
      hence "- (pi / 2) \<le> ?x2" and "?x2 \<le> pi / 2" using pi_ge_two unfolding real_of_float_mult Float_num by auto
hoelzl@29805
  1086
      hence "0 \<le> cos ?x2" by (rule cos_ge_zero)
hoelzl@31467
  1087
hoelzl@40881
  1088
      have "cos x \<le> (?ub_half y)"
hoelzl@29805
  1089
      proof -
wenzelm@32960
  1090
        have "0 \<le> real y" using `0 \<le> cos ?x2` ub by (rule order_trans)
wenzelm@32960
  1091
        from mult_mono[OF ub ub this `0 \<le> cos ?x2`]
wenzelm@32960
  1092
        have "cos ?x2 * cos ?x2 \<le> real y * real y" .
wenzelm@32960
  1093
        hence "2 * cos ?x2 * cos ?x2 \<le> 2 * real y * real y" by auto
hoelzl@40881
  1094
        hence "2 * cos (x / 2) * cos (x / 2) - 1 \<le> 2 * real y * real y - 1" unfolding Float_num real_of_float_mult by auto
wenzelm@32960
  1095
        thus ?thesis unfolding x_half real_of_float_mult Float_num real_of_float_sub by auto
hoelzl@29805
  1096
      qed
hoelzl@29805
  1097
    } note ub_half = this
hoelzl@31467
  1098
hoelzl@29805
  1099
    let ?x2 = "x * Float 1 -1"
hoelzl@29805
  1100
    let ?x4 = "x * Float 1 -1 * Float 1 -1"
hoelzl@31467
  1101
hoelzl@40881
  1102
    have "-pi \<le> x" using pi_ge_zero[THEN le_imp_neg_le, unfolded minus_zero] `0 \<le> real x` by (rule order_trans)
hoelzl@31467
  1103
hoelzl@29805
  1104
    show ?thesis
hoelzl@29805
  1105
    proof (cases "x < 1")
hoelzl@31098
  1106
      case True hence "real x \<le> 1" unfolding less_float_def by auto
hoelzl@40881
  1107
      have "0 \<le> real ?x2" and "?x2 \<le> pi / 2" using pi_ge_two `0 \<le> real x` unfolding real_of_float_mult Float_num using assms by auto
hoelzl@29805
  1108
      from cos_boundaries[OF this]
hoelzl@40881
  1109
      have lb: "(?lb_horner ?x2) \<le> ?cos ?x2" and ub: "?cos ?x2 \<le> (?ub_horner ?x2)" by auto
hoelzl@40881
  1110
hoelzl@40881
  1111
      have "(?lb x) \<le> ?cos x"
hoelzl@29805
  1112
      proof -
hoelzl@40881
  1113
        from lb_half[OF lb `-pi \<le> x` `x \<le> pi`]
wenzelm@32960
  1114
        show ?thesis unfolding lb_cos_def[where x=x] Let_def using `\<not> x < 0` `\<not> x < Float 1 -1` `x < 1` by auto
hoelzl@29805
  1115
      qed
hoelzl@40881
  1116
      moreover have "?cos x \<le> (?ub x)"
hoelzl@29805
  1117
      proof -
hoelzl@40881
  1118
        from ub_half[OF ub `-pi \<le> x` `x \<le> pi`]
wenzelm@32960
  1119
        show ?thesis unfolding ub_cos_def[where x=x] Let_def using `\<not> x < 0` `\<not> x < Float 1 -1` `x < 1` by auto
hoelzl@29805
  1120
      qed
hoelzl@29805
  1121
      ultimately show ?thesis by auto
hoelzl@29805
  1122
    next
hoelzl@29805
  1123
      case False
hoelzl@40881
  1124
      have "0 \<le> real ?x4" and "?x4 \<le> pi / 2" using pi_ge_two `0 \<le> real x` `x \<le> pi` unfolding real_of_float_mult Float_num by auto
hoelzl@29805
  1125
      from cos_boundaries[OF this]
hoelzl@40881
  1126
      have lb: "(?lb_horner ?x4) \<le> ?cos ?x4" and ub: "?cos ?x4 \<le> (?ub_horner ?x4)" by auto
hoelzl@31467
  1127
hoelzl@29805
  1128
      have eq_4: "?x2 * Float 1 -1 = x * Float 1 -2" by (cases x, auto simp add: times_float.simps)
hoelzl@31467
  1129
hoelzl@40881
  1130
      have "(?lb x) \<le> ?cos x"
hoelzl@29805
  1131
      proof -
hoelzl@40881
  1132
        have "-pi \<le> ?x2" and "?x2 \<le> pi" unfolding real_of_float_mult Float_num using pi_ge_two `0 \<le> real x` `x \<le> pi` by auto
hoelzl@40881
  1133
        from lb_half[OF lb_half[OF lb this] `-pi \<le> x` `x \<le> pi`, unfolded eq_4]
wenzelm@32960
  1134
        show ?thesis unfolding lb_cos_def[where x=x] if_not_P[OF `\<not> x < 0`] if_not_P[OF `\<not> x < Float 1 -1`] if_not_P[OF `\<not> x < 1`] Let_def .
hoelzl@29805
  1135
      qed
hoelzl@40881
  1136
      moreover have "?cos x \<le> (?ub x)"
hoelzl@29805
  1137
      proof -
hoelzl@40881
  1138
        have "-pi \<le> ?x2" and "?x2 \<le> pi" unfolding real_of_float_mult Float_num using pi_ge_two `0 \<le> real x` ` x \<le> pi` by auto
hoelzl@40881
  1139
        from ub_half[OF ub_half[OF ub this] `-pi \<le> x` `x \<le> pi`, unfolded eq_4]
wenzelm@32960
  1140
        show ?thesis unfolding ub_cos_def[where x=x] if_not_P[OF `\<not> x < 0`] if_not_P[OF `\<not> x < Float 1 -1`] if_not_P[OF `\<not> x < 1`] Let_def .
hoelzl@29805
  1141
      qed
hoelzl@29805
  1142
      ultimately show ?thesis by auto
hoelzl@29805
  1143
    qed
hoelzl@29805
  1144
  qed
hoelzl@29805
  1145
qed
hoelzl@29805
  1146
hoelzl@40881
  1147
lemma lb_cos_minus: assumes "-pi \<le> x" and "real x \<le> 0"
hoelzl@40881
  1148
  shows "cos (real(-x)) \<in> {(lb_cos prec (-x)) .. (ub_cos prec (-x))}"
hoelzl@29805
  1149
proof -
hoelzl@40881
  1150
  have "0 \<le> real (-x)" and "(-x) \<le> pi" using `-pi \<le> x` `real x \<le> 0` by auto
hoelzl@29805
  1151
  from lb_cos[OF this] show ?thesis .
hoelzl@29805
  1152
qed
hoelzl@29805
  1153
hoelzl@31467
  1154
definition bnds_cos :: "nat \<Rightarrow> float \<Rightarrow> float \<Rightarrow> float * float" where
hoelzl@31467
  1155
"bnds_cos prec lx ux = (let
hoelzl@31467
  1156
    lpi = round_down prec (lb_pi prec) ;
hoelzl@31467
  1157
    upi = round_up prec (ub_pi prec) ;
hoelzl@31467
  1158
    k = floor_fl (float_divr prec (lx + lpi) (2 * lpi)) ;
hoelzl@31467
  1159
    lx = lx - k * 2 * (if k < 0 then lpi else upi) ;
hoelzl@31467
  1160
    ux = ux - k * 2 * (if k < 0 then upi else lpi)
hoelzl@31467
  1161
  in   if - lpi \<le> lx \<and> ux \<le> 0    then (lb_cos prec (-lx), ub_cos prec (-ux))
hoelzl@31467
  1162
  else if 0 \<le> lx \<and> ux \<le> lpi      then (lb_cos prec ux, ub_cos prec lx)
hoelzl@31467
  1163
  else if - lpi \<le> lx \<and> ux \<le> lpi  then (min (lb_cos prec (-lx)) (lb_cos prec ux), Float 1 0)
hoelzl@31467
  1164
  else if 0 \<le> lx \<and> ux \<le> 2 * lpi  then (Float -1 0, max (ub_cos prec lx) (ub_cos prec (- (ux - 2 * lpi))))
hoelzl@31508
  1165
  else if -2 * lpi \<le> lx \<and> ux \<le> 0 then (Float -1 0, max (ub_cos prec (lx + 2 * lpi)) (ub_cos prec (-ux)))
hoelzl@31467
  1166
                                 else (Float -1 0, Float 1 0))"
hoelzl@29805
  1167
hoelzl@31467
  1168
lemma floor_int:
hoelzl@40881
  1169
  obtains k :: int where "real k = (floor_fl f)"
hoelzl@31467
  1170
proof -
hoelzl@40881
  1171
  assume *: "\<And> k :: int. real k = (floor_fl f) \<Longrightarrow> thesis"
hoelzl@31467
  1172
  obtain m e where fl: "Float m e = floor_fl f" by (cases "floor_fl f", auto)
hoelzl@31467
  1173
  from floor_pos_exp[OF this]
hoelzl@40881
  1174
  have "real (m* 2^(nat e)) = (floor_fl f)"
hoelzl@31467
  1175
    by (auto simp add: fl[symmetric] real_of_float_def pow2_def)
hoelzl@31467
  1176
  from *[OF this] show thesis by blast
hoelzl@31467
  1177
qed
hoelzl@29805
  1178
hoelzl@40881
  1179
lemma float_remove_real_numeral[simp]: "(number_of k :: float) = (number_of k :: real)"
hoelzl@31467
  1180
proof -
hoelzl@40881
  1181
  have "(number_of k :: float) = real k"
hoelzl@31467
  1182
    unfolding number_of_float_def real_of_float_def pow2_def by auto
hoelzl@40881
  1183
  also have "\<dots> = (number_of k :: int)"
hoelzl@31467
  1184
    by (simp add: number_of_is_id)
hoelzl@31467
  1185
  finally show ?thesis by auto
hoelzl@31467
  1186
qed
hoelzl@29805
  1187
hoelzl@40881
  1188
lemma cos_periodic_nat[simp]: fixes n :: nat shows "cos (x + n * (2 * pi)) = cos x"
hoelzl@31467
  1189
proof (induct n arbitrary: x)
hoelzl@31467
  1190
  case (Suc n)
hoelzl@40881
  1191
  have split_pi_off: "x + (Suc n) * (2 * pi) = (x + n * (2 * pi)) + 2 * pi"
huffman@36778
  1192
    unfolding Suc_eq_plus1 real_of_nat_add real_of_one left_distrib by auto
hoelzl@31467
  1193
  show ?case unfolding split_pi_off using Suc by auto
hoelzl@31467
  1194
qed auto
hoelzl@31467
  1195
hoelzl@40881
  1196
lemma cos_periodic_int[simp]: fixes i :: int shows "cos (x + i * (2 * pi)) = cos x"
hoelzl@31467
  1197
proof (cases "0 \<le> i")
hoelzl@40881
  1198
  case True hence i_nat: "real i = nat i" by auto
hoelzl@31467
  1199
  show ?thesis unfolding i_nat by auto
hoelzl@31467
  1200
next
hoelzl@40881
  1201
  case False hence i_nat: "i = - real (nat (-i))" by auto
hoelzl@40881
  1202
  have "cos x = cos (x + i * (2 * pi) - i * (2 * pi))" by auto
hoelzl@40881
  1203
  also have "\<dots> = cos (x + i * (2 * pi))"
hoelzl@31467
  1204
    unfolding i_nat mult_minus_left diff_minus_eq_add by (rule cos_periodic_nat)
hoelzl@31467
  1205
  finally show ?thesis by auto
hoelzl@29805
  1206
qed
hoelzl@29805
  1207
hoelzl@40881
  1208
lemma bnds_cos: "\<forall> (x::real) lx ux. (l, u) = bnds_cos prec lx ux \<and> x \<in> {lx .. ux} \<longrightarrow> l \<le> cos x \<and> cos x \<le> u"
hoelzl@31467
  1209
proof ((rule allI | rule impI | erule conjE) +)
hoelzl@40881
  1210
  fix x :: real fix lx ux
hoelzl@40881
  1211
  assume bnds: "(l, u) = bnds_cos prec lx ux" and x: "x \<in> {lx .. ux}"
hoelzl@31467
  1212
hoelzl@31467
  1213
  let ?lpi = "round_down prec (lb_pi prec)"
hoelzl@31467
  1214
  let ?upi = "round_up prec (ub_pi prec)"
hoelzl@31467
  1215
  let ?k = "floor_fl (float_divr prec (lx + ?lpi) (2 * ?lpi))"
hoelzl@31467
  1216
  let ?lx = "lx - ?k * 2 * (if ?k < 0 then ?lpi else ?upi)"
hoelzl@31467
  1217
  let ?ux = "ux - ?k * 2 * (if ?k < 0 then ?upi else ?lpi)"
hoelzl@31467
  1218
hoelzl@40881
  1219
  obtain k :: int where k: "k = real ?k" using floor_int .
hoelzl@40881
  1220
hoelzl@40881
  1221
  have upi: "pi \<le> ?upi" and lpi: "?lpi \<le> pi"
hoelzl@31467
  1222
    using round_up[of "ub_pi prec" prec] pi_boundaries[of prec]
hoelzl@31467
  1223
          round_down[of prec "lb_pi prec"] by auto
hoelzl@40881
  1224
  hence "?lx \<le> x - k * (2 * pi) \<and> x - k * (2 * pi) \<le> ?ux"
hoelzl@31467
  1225
    using x by (cases "k = 0") (auto intro!: add_mono
haftmann@37887
  1226
                simp add: diff_minus k[symmetric] less_float_def)
hoelzl@31467
  1227
  note lx = this[THEN conjunct1] and ux = this[THEN conjunct2]
hoelzl@40881
  1228
  hence lx_less_ux: "?lx \<le> real ?ux" by (rule order_trans)
hoelzl@40881
  1229
hoelzl@40881
  1230
  { assume "- ?lpi \<le> ?lx" and x_le_0: "x - k * (2 * pi) \<le> 0"
hoelzl@31467
  1231
    with lpi[THEN le_imp_neg_le] lx
hoelzl@40881
  1232
    have pi_lx: "- pi \<le> ?lx" and lx_0: "real ?lx \<le> 0"
hoelzl@31467
  1233
      by (simp_all add: le_float_def)
hoelzl@29805
  1234
hoelzl@40881
  1235
    have "(lb_cos prec (- ?lx)) \<le> cos (real (- ?lx))"
hoelzl@31467
  1236
      using lb_cos_minus[OF pi_lx lx_0] by simp
hoelzl@40881
  1237
    also have "\<dots> \<le> cos (x + (-k) * (2 * pi))"
hoelzl@31467
  1238
      using cos_monotone_minus_pi_0'[OF pi_lx lx x_le_0]
hoelzl@31467
  1239
      by (simp only: real_of_float_minus real_of_int_minus
haftmann@37887
  1240
        cos_minus diff_minus mult_minus_left)
hoelzl@40881
  1241
    finally have "(lb_cos prec (- ?lx)) \<le> cos x"
hoelzl@31467
  1242
      unfolding cos_periodic_int . }
hoelzl@31467
  1243
  note negative_lx = this
hoelzl@31467
  1244
hoelzl@40881
  1245
  { assume "0 \<le> ?lx" and pi_x: "x - k * (2 * pi) \<le> pi"
hoelzl@31467
  1246
    with lx
hoelzl@40881
  1247
    have pi_lx: "?lx \<le> pi" and lx_0: "0 \<le> real ?lx"
hoelzl@31467
  1248
      by (auto simp add: le_float_def)
hoelzl@29805
  1249
hoelzl@40881
  1250
    have "cos (x + (-k) * (2 * pi)) \<le> cos ?lx"
hoelzl@31467
  1251
      using cos_monotone_0_pi'[OF lx_0 lx pi_x]
hoelzl@31467
  1252
      by (simp only: real_of_float_minus real_of_int_minus
haftmann@37887
  1253
        cos_minus diff_minus mult_minus_left)
hoelzl@40881
  1254
    also have "\<dots> \<le> (ub_cos prec ?lx)"
hoelzl@31467
  1255
      using lb_cos[OF lx_0 pi_lx] by simp
hoelzl@40881
  1256
    finally have "cos x \<le> (ub_cos prec ?lx)"
hoelzl@31467
  1257
      unfolding cos_periodic_int . }
hoelzl@31467
  1258
  note positive_lx = this
hoelzl@31467
  1259
hoelzl@40881
  1260
  { assume pi_x: "- pi \<le> x - k * (2 * pi)" and "?ux \<le> 0"
hoelzl@31467
  1261
    with ux
hoelzl@40881
  1262
    have pi_ux: "- pi \<le> ?ux" and ux_0: "real ?ux \<le> 0"
hoelzl@31467
  1263
      by (simp_all add: le_float_def)
hoelzl@29805
  1264
hoelzl@40881
  1265
    have "cos (x + (-k) * (2 * pi)) \<le> cos (real (- ?ux))"
hoelzl@31467
  1266
      using cos_monotone_minus_pi_0'[OF pi_x ux ux_0]
hoelzl@31467
  1267
      by (simp only: real_of_float_minus real_of_int_minus
haftmann@37887
  1268
          cos_minus diff_minus mult_minus_left)
hoelzl@40881
  1269
    also have "\<dots> \<le> (ub_cos prec (- ?ux))"
hoelzl@31467
  1270
      using lb_cos_minus[OF pi_ux ux_0, of prec] by simp
hoelzl@40881
  1271
    finally have "cos x \<le> (ub_cos prec (- ?ux))"
hoelzl@31467
  1272
      unfolding cos_periodic_int . }
hoelzl@31467
  1273
  note negative_ux = this
hoelzl@31467
  1274
hoelzl@40881
  1275
  { assume "?ux \<le> ?lpi" and x_ge_0: "0 \<le> x - k * (2 * pi)"
hoelzl@31467
  1276
    with lpi ux
hoelzl@40881
  1277
    have pi_ux: "?ux \<le> pi" and ux_0: "0 \<le> real ?ux"
hoelzl@31467
  1278
      by (simp_all add: le_float_def)
hoelzl@31467
  1279
hoelzl@40881
  1280
    have "(lb_cos prec ?ux) \<le> cos ?ux"
hoelzl@31467
  1281
      using lb_cos[OF ux_0 pi_ux] by simp
hoelzl@40881
  1282
    also have "\<dots> \<le> cos (x + (-k) * (2 * pi))"
hoelzl@31467
  1283
      using cos_monotone_0_pi'[OF x_ge_0 ux pi_ux]
hoelzl@31467
  1284
      by (simp only: real_of_float_minus real_of_int_minus
haftmann@37887
  1285
        cos_minus diff_minus mult_minus_left)
hoelzl@40881
  1286
    finally have "(lb_cos prec ?ux) \<le> cos x"
hoelzl@31467
  1287
      unfolding cos_periodic_int . }
hoelzl@31467
  1288
  note positive_ux = this
hoelzl@31467
  1289
hoelzl@40881
  1290
  show "l \<le> cos x \<and> cos x \<le> u"
hoelzl@31467
  1291
  proof (cases "- ?lpi \<le> ?lx \<and> ?ux \<le> 0")
hoelzl@31467
  1292
    case True with bnds
hoelzl@31467
  1293
    have l: "l = lb_cos prec (-?lx)"
hoelzl@31467
  1294
      and u: "u = ub_cos prec (-?ux)"
hoelzl@31467
  1295
      by (auto simp add: bnds_cos_def Let_def)
hoelzl@29805
  1296
hoelzl@31467
  1297
    from True lpi[THEN le_imp_neg_le] lx ux
hoelzl@40881
  1298
    have "- pi \<le> x - k * (2 * pi)"
hoelzl@40881
  1299
      and "x - k * (2 * pi) \<le> 0"
hoelzl@31467
  1300
      by (auto simp add: le_float_def)
hoelzl@31467
  1301
    with True negative_ux negative_lx
hoelzl@31467
  1302
    show ?thesis unfolding l u by simp
hoelzl@31467
  1303
  next case False note 1 = this show ?thesis
hoelzl@31467
  1304
  proof (cases "0 \<le> ?lx \<and> ?ux \<le> ?lpi")
hoelzl@31467
  1305
    case True with bnds 1
hoelzl@31467
  1306
    have l: "l = lb_cos prec ?ux"
hoelzl@31467
  1307
      and u: "u = ub_cos prec ?lx"
hoelzl@31467
  1308
      by (auto simp add: bnds_cos_def Let_def)
hoelzl@29805
  1309
hoelzl@31467
  1310
    from True lpi lx ux
hoelzl@40881
  1311
    have "0 \<le> x - k * (2 * pi)"
hoelzl@40881
  1312
      and "x - k * (2 * pi) \<le> pi"
hoelzl@31467
  1313
      by (auto simp add: le_float_def)
hoelzl@31467
  1314
    with True positive_ux positive_lx
hoelzl@31467
  1315
    show ?thesis unfolding l u by simp
hoelzl@31467
  1316
  next case False note 2 = this show ?thesis
hoelzl@31467
  1317
  proof (cases "- ?lpi \<le> ?lx \<and> ?ux \<le> ?lpi")
hoelzl@31467
  1318
    case True note Cond = this with bnds 1 2
hoelzl@31467
  1319
    have l: "l = min (lb_cos prec (-?lx)) (lb_cos prec ?ux)"
hoelzl@31467
  1320
      and u: "u = Float 1 0"
hoelzl@31467
  1321
      by (auto simp add: bnds_cos_def Let_def)
hoelzl@29805
  1322
hoelzl@31467
  1323
    show ?thesis unfolding u l using negative_lx positive_ux Cond
hoelzl@40881
  1324
      by (cases "x - k * (2 * pi) < 0", simp_all add: real_of_float_min)
hoelzl@31467
  1325
  next case False note 3 = this show ?thesis
hoelzl@31467
  1326
  proof (cases "0 \<le> ?lx \<and> ?ux \<le> 2 * ?lpi")
hoelzl@31467
  1327
    case True note Cond = this with bnds 1 2 3
hoelzl@31467
  1328
    have l: "l = Float -1 0"
hoelzl@31467
  1329
      and u: "u = max (ub_cos prec ?lx) (ub_cos prec (- (?ux - 2 * ?lpi)))"
hoelzl@31467
  1330
      by (auto simp add: bnds_cos_def Let_def)
hoelzl@31467
  1331
hoelzl@31467
  1332
    have "cos x \<le> real u"
hoelzl@40881
  1333
    proof (cases "x - k * (2 * pi) < pi")
hoelzl@40881
  1334
      case True hence "x - k * (2 * pi) \<le> pi" by simp
hoelzl@31467
  1335
      from positive_lx[OF Cond[THEN conjunct1] this]
hoelzl@31467
  1336
      show ?thesis unfolding u by (simp add: real_of_float_max)
hoelzl@29805
  1337
    next
hoelzl@40881
  1338
      case False hence "pi \<le> x - k * (2 * pi)" by simp
hoelzl@40881
  1339
      hence pi_x: "- pi \<le> x - k * (2 * pi) - 2 * pi" by simp
hoelzl@40881
  1340
hoelzl@40881
  1341
      have "?ux \<le> 2 * pi" using Cond lpi by (auto simp add: le_float_def)
hoelzl@40881
  1342
      hence "x - k * (2 * pi) - 2 * pi \<le> 0" using ux by simp
hoelzl@31467
  1343
hoelzl@31467
  1344
      have ux_0: "real (?ux - 2 * ?lpi) \<le> 0"
wenzelm@32960
  1345
        using Cond by (auto simp add: le_float_def)
hoelzl@31467
  1346
hoelzl@31467
  1347
      from 2 and Cond have "\<not> ?ux \<le> ?lpi" by auto
hoelzl@31467
  1348
      hence "- ?lpi \<le> ?ux - 2 * ?lpi" by (auto simp add: le_float_def)
hoelzl@40881
  1349
      hence pi_ux: "- pi \<le> (?ux - 2 * ?lpi)"
wenzelm@32960
  1350
        using lpi[THEN le_imp_neg_le] by (auto simp add: le_float_def)
hoelzl@31467
  1351
hoelzl@40881
  1352
      have x_le_ux: "x - k * (2 * pi) - 2 * pi \<le> (?ux - 2 * ?lpi)"
wenzelm@32960
  1353
        using ux lpi by auto
hoelzl@31467
  1354
hoelzl@40881
  1355
      have "cos x = cos (x + (-k) * (2 * pi) + (-1::int) * (2 * pi))"
wenzelm@32960
  1356
        unfolding cos_periodic_int ..
hoelzl@40881
  1357
      also have "\<dots> \<le> cos ((?ux - 2 * ?lpi))"
wenzelm@32960
  1358
        using cos_monotone_minus_pi_0'[OF pi_x x_le_ux ux_0]
wenzelm@32960
  1359
        by (simp only: real_of_float_minus real_of_int_minus real_of_one
haftmann@37887
  1360
            number_of_Min diff_minus mult_minus_left mult_1_left)
hoelzl@40881
  1361
      also have "\<dots> = cos ((- (?ux - 2 * ?lpi)))"
wenzelm@32960
  1362
        unfolding real_of_float_minus cos_minus ..
hoelzl@40881
  1363
      also have "\<dots> \<le> (ub_cos prec (- (?ux - 2 * ?lpi)))"
wenzelm@32960
  1364
        using lb_cos_minus[OF pi_ux ux_0] by simp
hoelzl@31467
  1365
      finally show ?thesis unfolding u by (simp add: real_of_float_max)
hoelzl@29805
  1366
    qed
hoelzl@31467
  1367
    thus ?thesis unfolding l by auto
hoelzl@31508
  1368
  next case False note 4 = this show ?thesis
hoelzl@31508
  1369
  proof (cases "-2 * ?lpi \<le> ?lx \<and> ?ux \<le> 0")
hoelzl@31508
  1370
    case True note Cond = this with bnds 1 2 3 4
hoelzl@31508
  1371
    have l: "l = Float -1 0"
hoelzl@31508
  1372
      and u: "u = max (ub_cos prec (?lx + 2 * ?lpi)) (ub_cos prec (-?ux))"
hoelzl@31508
  1373
      by (auto simp add: bnds_cos_def Let_def)
hoelzl@31508
  1374
hoelzl@40881
  1375
    have "cos x \<le> u"
hoelzl@40881
  1376
    proof (cases "-pi < x - k * (2 * pi)")
hoelzl@40881
  1377
      case True hence "-pi \<le> x - k * (2 * pi)" by simp
hoelzl@31508
  1378
      from negative_ux[OF this Cond[THEN conjunct2]]
hoelzl@31508
  1379
      show ?thesis unfolding u by (simp add: real_of_float_max)
hoelzl@31508
  1380
    next
hoelzl@40881
  1381
      case False hence "x - k * (2 * pi) \<le> -pi" by simp
hoelzl@40881
  1382
      hence pi_x: "x - k * (2 * pi) + 2 * pi \<le> pi" by simp
hoelzl@40881
  1383
hoelzl@40881
  1384
      have "-2 * pi \<le> ?lx" using Cond lpi by (auto simp add: le_float_def)
hoelzl@40881
  1385
hoelzl@40881
  1386
      hence "0 \<le> x - k * (2 * pi) + 2 * pi" using lx by simp
hoelzl@31508
  1387
hoelzl@31508
  1388
      have lx_0: "0 \<le> real (?lx + 2 * ?lpi)"
wenzelm@32960
  1389
        using Cond lpi by (auto simp add: le_float_def)
hoelzl@31508
  1390
hoelzl@31508
  1391
      from 1 and Cond have "\<not> -?lpi \<le> ?lx" by auto
hoelzl@31508
  1392
      hence "?lx + 2 * ?lpi \<le> ?lpi" by (auto simp add: le_float_def)
hoelzl@40881
  1393
      hence pi_lx: "(?lx + 2 * ?lpi) \<le> pi"
wenzelm@32960
  1394
        using lpi[THEN le_imp_neg_le] by (auto simp add: le_float_def)
hoelzl@31508
  1395
hoelzl@40881
  1396
      have lx_le_x: "(?lx + 2 * ?lpi) \<le> x - k * (2 * pi) + 2 * pi"
wenzelm@32960
  1397
        using lx lpi by auto
hoelzl@31508
  1398
hoelzl@40881
  1399
      have "cos x = cos (x + (-k) * (2 * pi) + (1 :: int) * (2 * pi))"
wenzelm@32960
  1400
        unfolding cos_periodic_int ..
hoelzl@40881
  1401
      also have "\<dots> \<le> cos ((?lx + 2 * ?lpi))"
wenzelm@32960
  1402
        using cos_monotone_0_pi'[OF lx_0 lx_le_x pi_x]
wenzelm@32960
  1403
        by (simp only: real_of_float_minus real_of_int_minus real_of_one
haftmann@37887
  1404
          number_of_Min diff_minus mult_minus_left mult_1_left)
hoelzl@40881
  1405
      also have "\<dots> \<le> (ub_cos prec (?lx + 2 * ?lpi))"
wenzelm@32960
  1406
        using lb_cos[OF lx_0 pi_lx] by simp
hoelzl@31508
  1407
      finally show ?thesis unfolding u by (simp add: real_of_float_max)
hoelzl@31508
  1408
    qed
hoelzl@31508
  1409
    thus ?thesis unfolding l by auto
hoelzl@29805
  1410
  next
hoelzl@31508
  1411
    case False with bnds 1 2 3 4 show ?thesis by (auto simp add: bnds_cos_def Let_def)
hoelzl@31508
  1412
  qed qed qed qed qed
hoelzl@29805
  1413
qed
hoelzl@29805
  1414
hoelzl@29805
  1415
section "Exponential function"
hoelzl@29805
  1416
hoelzl@29805
  1417
subsection "Compute the series of the exponential function"
hoelzl@29805
  1418
hoelzl@29805
  1419
fun ub_exp_horner :: "nat \<Rightarrow> nat \<Rightarrow> nat \<Rightarrow> nat \<Rightarrow> float \<Rightarrow> float" and lb_exp_horner :: "nat \<Rightarrow> nat \<Rightarrow> nat \<Rightarrow> nat \<Rightarrow> float \<Rightarrow> float" where
hoelzl@29805
  1420
"ub_exp_horner prec 0 i k x       = 0" |
hoelzl@29805
  1421
"ub_exp_horner prec (Suc n) i k x = rapprox_rat prec 1 (int k) + x * lb_exp_horner prec n (i + 1) (k * i) x" |
hoelzl@29805
  1422
"lb_exp_horner prec 0 i k x       = 0" |
hoelzl@29805
  1423
"lb_exp_horner prec (Suc n) i k x = lapprox_rat prec 1 (int k) + x * ub_exp_horner prec n (i + 1) (k * i) x"
hoelzl@29805
  1424
hoelzl@31098
  1425
lemma bnds_exp_horner: assumes "real x \<le> 0"
hoelzl@40881
  1426
  shows "exp x \<in> { lb_exp_horner prec (get_even n) 1 1 x .. ub_exp_horner prec (get_odd n) 1 1 x }"
hoelzl@29805
  1427
proof -
hoelzl@29805
  1428
  { fix n
haftmann@30971
  1429
    have F: "\<And> m. ((\<lambda>i. i + 1) ^^ n) m = n + m" by (induct n, auto)
haftmann@30971
  1430
    have "fact (Suc n) = fact n * ((\<lambda>i. i + 1) ^^ n) 1" unfolding F by auto } note f_eq = this
hoelzl@31467
  1431
hoelzl@29805
  1432
  note bounds = horner_bounds_nonpos[where f="fact" and lb="lb_exp_horner prec" and ub="ub_exp_horner prec" and j'=0 and s=1,
hoelzl@29805
  1433
    OF assms f_eq lb_exp_horner.simps ub_exp_horner.simps]
hoelzl@29805
  1434
hoelzl@40881
  1435
  { have "lb_exp_horner prec (get_even n) 1 1 x \<le> (\<Sum>j = 0..<get_even n. 1 / real (fact j) * real x ^ j)"
hoelzl@29805
  1436
      using bounds(1) by auto
hoelzl@40881
  1437
    also have "\<dots> \<le> exp x"
hoelzl@29805
  1438
    proof -
hoelzl@40881
  1439
      obtain t where "\<bar>t\<bar> \<le> \<bar>real x\<bar>" and "exp x = (\<Sum>m = 0..<get_even n. real x ^ m / real (fact m)) + exp t / real (fact (get_even n)) * (real x) ^ (get_even n)"
wenzelm@32960
  1440
        using Maclaurin_exp_le by blast
hoelzl@31098
  1441
      moreover have "0 \<le> exp t / real (fact (get_even n)) * (real x) ^ (get_even n)"
wenzelm@32960
  1442
        by (auto intro!: mult_nonneg_nonneg divide_nonneg_pos simp add: get_even zero_le_even_power exp_gt_zero)
hoelzl@29805
  1443
      ultimately show ?thesis
haftmann@35028
  1444
        using get_odd exp_gt_zero by (auto intro!: mult_nonneg_nonneg)
hoelzl@29805
  1445
    qed
hoelzl@40881
  1446
    finally have "lb_exp_horner prec (get_even n) 1 1 x \<le> exp x" .
hoelzl@29805
  1447
  } moreover
hoelzl@31809
  1448
  {
hoelzl@31098
  1449
    have x_less_zero: "real x ^ get_odd n \<le> 0"
hoelzl@31098
  1450
    proof (cases "real x = 0")
hoelzl@29805
  1451
      case True
hoelzl@29805
  1452
      have "(get_odd n) \<noteq> 0" using get_odd[THEN odd_pos] by auto
hoelzl@29805
  1453
      thus ?thesis unfolding True power_0_left by auto
hoelzl@29805
  1454
    next
hoelzl@31098
  1455
      case False hence "real x < 0" using `real x \<le> 0` by auto
hoelzl@31098
  1456
      show ?thesis by (rule less_imp_le, auto simp add: power_less_zero_eq get_odd `real x < 0`)
hoelzl@29805
  1457
    qed
hoelzl@29805
  1458
hoelzl@40881
  1459
    obtain t where "\<bar>t\<bar> \<le> \<bar>real x\<bar>" and "exp x = (\<Sum>m = 0..<get_odd n. (real x) ^ m / real (fact m)) + exp t / real (fact (get_odd n)) * (real x) ^ (get_odd n)"
hoelzl@29805
  1460
      using Maclaurin_exp_le by blast
hoelzl@31098
  1461
    moreover have "exp t / real (fact (get_odd n)) * (real x) ^ (get_odd n) \<le> 0"
hoelzl@29805
  1462
      by (auto intro!: mult_nonneg_nonpos divide_nonpos_pos simp add: x_less_zero exp_gt_zero)
hoelzl@40881
  1463
    ultimately have "exp x \<le> (\<Sum>j = 0..<get_odd n. 1 / real (fact j) * real x ^ j)"
haftmann@35028
  1464
      using get_odd exp_gt_zero by (auto intro!: mult_nonneg_nonneg)
hoelzl@40881
  1465
    also have "\<dots> \<le> ub_exp_horner prec (get_odd n) 1 1 x"
hoelzl@29805
  1466
      using bounds(2) by auto
hoelzl@40881
  1467
    finally have "exp x \<le> ub_exp_horner prec (get_odd n) 1 1 x" .
hoelzl@29805
  1468
  } ultimately show ?thesis by auto
hoelzl@29805
  1469
qed
hoelzl@29805
  1470
hoelzl@29805
  1471
subsection "Compute the exponential function on the entire domain"
hoelzl@29805
  1472
hoelzl@29805
  1473
function ub_exp :: "nat \<Rightarrow> float \<Rightarrow> float" and lb_exp :: "nat \<Rightarrow> float \<Rightarrow> float" where
hoelzl@29805
  1474
"lb_exp prec x = (if 0 < x then float_divl prec 1 (ub_exp prec (-x))
hoelzl@31809
  1475
             else let
hoelzl@29805
  1476
                horner = (\<lambda> x. let  y = lb_exp_horner prec (get_even (prec + 2)) 1 1 x  in if y \<le> 0 then Float 1 -2 else y)
hoelzl@29805
  1477
             in if x < - 1 then (case floor_fl x of (Float m e) \<Rightarrow> (horner (float_divl prec x (- Float m e))) ^ (nat (-m) * 2 ^ nat e))
hoelzl@29805
  1478
                           else horner x)" |
hoelzl@29805
  1479
"ub_exp prec x = (if 0 < x    then float_divr prec 1 (lb_exp prec (-x))
hoelzl@31809
  1480
             else if x < - 1  then (case floor_fl x of (Float m e) \<Rightarrow>
hoelzl@29805
  1481
                                    (ub_exp_horner prec (get_odd (prec + 2)) 1 1 (float_divr prec x (- Float m e))) ^ (nat (-m) * 2 ^ nat e))
hoelzl@29805
  1482
                              else ub_exp_horner prec (get_odd (prec + 2)) 1 1 x)"
hoelzl@29805
  1483
by pat_completeness auto
hoelzl@29805
  1484
termination by (relation "measure (\<lambda> v. let (prec, x) = sum_case id id v in (if 0 < x then 1 else 0))", auto simp add: less_float_def)
hoelzl@29805
  1485
hoelzl@29805
  1486
lemma exp_m1_ge_quarter: "(1 / 4 :: real) \<le> exp (- 1)"
hoelzl@29805
  1487
proof -
hoelzl@29805
  1488
  have eq4: "4 = Suc (Suc (Suc (Suc 0)))" by auto
hoelzl@29805
  1489
hoelzl@40881
  1490
  have "1 / 4 = (Float 1 -2)" unfolding Float_num by auto
hoelzl@40881
  1491
  also have "\<dots> \<le> lb_exp_horner 1 (get_even 4) 1 1 (- 1)"
hoelzl@31809
  1492
    unfolding get_even_def eq4
hoelzl@29805
  1493
    by (auto simp add: lapprox_posrat_def rapprox_posrat_def normfloat.simps)
hoelzl@40881
  1494
  also have "\<dots> \<le> exp (- 1 :: float)" using bnds_exp_horner[where x="- 1"] by auto
hoelzl@31809
  1495
  finally show ?thesis unfolding real_of_float_minus real_of_float_1 .
hoelzl@29805
  1496
qed
hoelzl@29805
  1497
hoelzl@29805
  1498
lemma lb_exp_pos: assumes "\<not> 0 < x" shows "0 < lb_exp prec x"
hoelzl@29805
  1499
proof -
hoelzl@29805
  1500
  let "?lb_horner x" = "lb_exp_horner prec (get_even (prec + 2)) 1 1 x"
hoelzl@29805
  1501
  let "?horner x" = "let  y = ?lb_horner x  in if y \<le> 0 then Float 1 -2 else y"
hoelzl@29805
  1502
  have pos_horner: "\<And> x. 0 < ?horner x" unfolding Let_def by (cases "?lb_horner x \<le> 0", auto simp add: le_float_def less_float_def)
hoelzl@29805
  1503
  moreover { fix x :: float fix num :: nat
hoelzl@31098
  1504
    have "0 < real (?horner x) ^ num" using `0 < ?horner x`[unfolded less_float_def real_of_float_0] by (rule zero_less_power)
hoelzl@40881
  1505
    also have "\<dots> = (?horner x) ^ num" using float_power by auto
hoelzl@31098
  1506
    finally have "0 < real ((?horner x) ^ num)" .
hoelzl@29805
  1507
  }
hoelzl@29805
  1508
  ultimately show ?thesis
haftmann@30968
  1509
    unfolding lb_exp.simps if_not_P[OF `\<not> 0 < x`] Let_def
haftmann@30968
  1510
    by (cases "floor_fl x", cases "x < - 1", auto simp add: float_power le_float_def less_float_def)
hoelzl@29805
  1511
qed
hoelzl@29805
  1512
hoelzl@29805
  1513
lemma exp_boundaries': assumes "x \<le> 0"
hoelzl@40881
  1514
  shows "exp x \<in> { (lb_exp prec x) .. (ub_exp prec x)}"
hoelzl@29805
  1515
proof -
hoelzl@29805
  1516
  let "?lb_exp_horner x" = "lb_exp_horner prec (get_even (prec + 2)) 1 1 x"
hoelzl@29805
  1517
  let "?ub_exp_horner x" = "ub_exp_horner prec (get_odd (prec + 2)) 1 1 x"
hoelzl@29805
  1518
hoelzl@31098
  1519
  have "real x \<le> 0" and "\<not> x > 0" using `x \<le> 0` unfolding le_float_def less_float_def by auto
hoelzl@29805
  1520
  show ?thesis
hoelzl@29805
  1521
  proof (cases "x < - 1")
hoelzl@31098
  1522
    case False hence "- 1 \<le> real x" unfolding less_float_def by auto
hoelzl@29805
  1523
    show ?thesis
hoelzl@29805
  1524
    proof (cases "?lb_exp_horner x \<le> 0")
hoelzl@31098
  1525
      from `\<not> x < - 1` have "- 1 \<le> real x" unfolding less_float_def by auto
hoelzl@40881
  1526
      hence "exp (- 1) \<le> exp x" unfolding exp_le_cancel_iff .
hoelzl@29805
  1527
      from order_trans[OF exp_m1_ge_quarter this]
hoelzl@40881
  1528
      have "Float 1 -2 \<le> exp x" unfolding Float_num .
hoelzl@29805
  1529
      moreover case True
hoelzl@31098
  1530
      ultimately show ?thesis using bnds_exp_horner `real x \<le> 0` `\<not> x > 0` `\<not> x < - 1` by auto
hoelzl@29805
  1531
    next
hoelzl@31098
  1532
      case False thus ?thesis using bnds_exp_horner `real x \<le> 0` `\<not> x > 0` `\<not> x < - 1` by (auto simp add: Let_def)
hoelzl@29805
  1533
    qed
hoelzl@29805
  1534
  next
hoelzl@29805
  1535
    case True
hoelzl@31809
  1536
hoelzl@29805
  1537
    obtain m e where Float_floor: "floor_fl x = Float m e" by (cases "floor_fl x", auto)
hoelzl@29805
  1538
    let ?num = "nat (- m) * 2 ^ nat e"
hoelzl@31809
  1539
hoelzl@31098
  1540
    have "real (floor_fl x) < - 1" using floor_fl `x < - 1` unfolding le_float_def less_float_def real_of_float_minus real_of_float_1 by (rule order_le_less_trans)
hoelzl@31098
  1541
    hence "real (floor_fl x) < 0" unfolding Float_floor real_of_float_simp using zero_less_pow2[of xe] by auto
hoelzl@29805
  1542
    hence "m < 0"
hoelzl@31098
  1543
      unfolding less_float_def real_of_float_0 Float_floor real_of_float_simp
huffman@36778
  1544
      unfolding pos_prod_lt[OF zero_less_pow2[of e], unfolded mult_commute] by auto
hoelzl@29805
  1545
    hence "1 \<le> - m" by auto
hoelzl@29805
  1546
    hence "0 < nat (- m)" by auto
hoelzl@29805
  1547
    moreover
hoelzl@29805
  1548
    have "0 \<le> e" using floor_pos_exp Float_floor[symmetric] by auto
hoelzl@29805
  1549
    hence "(0::nat) < 2 ^ nat e" by auto
hoelzl@29805
  1550
    ultimately have "0 < ?num"  by auto
hoelzl@29805
  1551
    hence "real ?num \<noteq> 0" by auto
hoelzl@40881
  1552
    have e_nat: "(nat e) = e" using `0 \<le> e` by auto
hoelzl@40881
  1553
    have num_eq: "real ?num = - floor_fl x" using `0 < nat (- m)`
huffman@35346
  1554
      unfolding Float_floor real_of_float_minus real_of_float_simp real_of_nat_mult pow2_int[of "nat e", unfolded e_nat] real_of_nat_power by auto
hoelzl@31098
  1555
    have "0 < - floor_fl x" using `0 < ?num`[unfolded real_of_nat_less_iff[symmetric]] unfolding less_float_def num_eq[symmetric] real_of_float_0 real_of_nat_zero .
hoelzl@31098
  1556
    hence "real (floor_fl x) < 0" unfolding less_float_def by auto
hoelzl@31809
  1557
hoelzl@40881
  1558
    have "exp x \<le> ub_exp prec x"
hoelzl@29805
  1559
    proof -
hoelzl@31809
  1560
      have div_less_zero: "real (float_divr prec x (- floor_fl x)) \<le> 0"
wenzelm@32960
  1561
        using float_divr_nonpos_pos_upper_bound[OF `x \<le> 0` `0 < - floor_fl x`] unfolding le_float_def real_of_float_0 .
hoelzl@31809
  1562
hoelzl@40881
  1563
      have "exp x = exp (?num * (x / ?num))" using `real ?num \<noteq> 0` by auto
hoelzl@40881
  1564
      also have "\<dots> = exp (x / ?num) ^ ?num" unfolding exp_real_of_nat_mult ..
hoelzl@40881
  1565
      also have "\<dots> \<le> exp (float_divr prec x (- floor_fl x)) ^ ?num" unfolding num_eq
wenzelm@32960
  1566
        by (rule power_mono, rule exp_le_cancel_iff[THEN iffD2], rule float_divr) auto
hoelzl@40881
  1567
      also have "\<dots> \<le> (?ub_exp_horner (float_divr prec x (- floor_fl x))) ^ ?num" unfolding float_power
wenzelm@32960
  1568
        by (rule power_mono, rule bnds_exp_horner[OF div_less_zero, unfolded atLeastAtMost_iff, THEN conjunct2], auto)
hoelzl@29805
  1569
      finally show ?thesis unfolding ub_exp.simps if_not_P[OF `\<not> 0 < x`] if_P[OF `x < - 1`] float.cases Float_floor Let_def .
hoelzl@29805
  1570
    qed
hoelzl@31809
  1571
    moreover
hoelzl@40881
  1572
    have "lb_exp prec x \<le> exp x"
hoelzl@29805
  1573
    proof -
hoelzl@29805
  1574
      let ?divl = "float_divl prec x (- Float m e)"
hoelzl@29805
  1575
      let ?horner = "?lb_exp_horner ?divl"
hoelzl@31809
  1576
hoelzl@29805
  1577
      show ?thesis
hoelzl@29805
  1578
      proof (cases "?horner \<le> 0")
wenzelm@32960
  1579
        case False hence "0 \<le> real ?horner" unfolding le_float_def by auto
wenzelm@32960
  1580
wenzelm@32960
  1581
        have div_less_zero: "real (float_divl prec x (- floor_fl x)) \<le> 0"
wenzelm@32960
  1582
          using `real (floor_fl x) < 0` `real x \<le> 0` by (auto intro!: order_trans[OF float_divl] divide_nonpos_neg)
wenzelm@32960
  1583
hoelzl@40881
  1584
        have "(?lb_exp_horner (float_divl prec x (- floor_fl x))) ^ ?num \<le>
hoelzl@40881
  1585
          exp (float_divl prec x (- floor_fl x)) ^ ?num" unfolding float_power
wenzelm@32960
  1586
          using `0 \<le> real ?horner`[unfolded Float_floor[symmetric]] bnds_exp_horner[OF div_less_zero, unfolded atLeastAtMost_iff, THEN conjunct1] by (auto intro!: power_mono)
hoelzl@40881
  1587
        also have "\<dots> \<le> exp (x / ?num) ^ ?num" unfolding num_eq
wenzelm@32960
  1588
          using float_divl by (auto intro!: power_mono simp del: real_of_float_minus)
hoelzl@40881
  1589
        also have "\<dots> = exp (?num * (x / ?num))" unfolding exp_real_of_nat_mult ..
hoelzl@40881
  1590
        also have "\<dots> = exp x" using `real ?num \<noteq> 0` by auto
wenzelm@32960
  1591
        finally show ?thesis
wenzelm@32960
  1592
          unfolding lb_exp.simps if_not_P[OF `\<not> 0 < x`] if_P[OF `x < - 1`] float.cases Float_floor Let_def if_not_P[OF False] by auto
hoelzl@29805
  1593
      next
wenzelm@32960
  1594
        case True
wenzelm@32960
  1595
        have "real (floor_fl x) \<noteq> 0" and "real (floor_fl x) \<le> 0" using `real (floor_fl x) < 0` by auto
wenzelm@32960
  1596
        from divide_right_mono_neg[OF floor_fl[of x] `real (floor_fl x) \<le> 0`, unfolded divide_self[OF `real (floor_fl x) \<noteq> 0`]]
hoelzl@40881
  1597
        have "- 1 \<le> x / (- floor_fl x)" unfolding real_of_float_minus by auto
wenzelm@32960
  1598
        from order_trans[OF exp_m1_ge_quarter this[unfolded exp_le_cancel_iff[where x="- 1", symmetric]]]
hoelzl@40881
  1599
        have "Float 1 -2 \<le> exp (x / (- floor_fl x))" unfolding Float_num .
hoelzl@40881
  1600
        hence "real (Float 1 -2) ^ ?num \<le> exp (x / (- floor_fl x)) ^ ?num"
wenzelm@32960
  1601
          by (auto intro!: power_mono simp add: Float_num)
hoelzl@40881
  1602
        also have "\<dots> = exp x" unfolding num_eq exp_real_of_nat_mult[symmetric] using `real (floor_fl x) \<noteq> 0` by auto
wenzelm@32960
  1603
        finally show ?thesis
wenzelm@32960
  1604
          unfolding lb_exp.simps if_not_P[OF `\<not> 0 < x`] if_P[OF `x < - 1`] float.cases Float_floor Let_def if_P[OF True] float_power .
hoelzl@29805
  1605
      qed
hoelzl@29805
  1606
    qed
hoelzl@29805
  1607
    ultimately show ?thesis by auto
hoelzl@29805
  1608
  qed
hoelzl@29805
  1609
qed
hoelzl@29805
  1610
hoelzl@40881
  1611
lemma exp_boundaries: "exp x \<in> { lb_exp prec x .. ub_exp prec x }"
hoelzl@29805
  1612
proof -
hoelzl@29805
  1613
  show ?thesis
hoelzl@29805
  1614
  proof (cases "0 < x")
hoelzl@31809
  1615
    case False hence "x \<le> 0" unfolding less_float_def le_float_def by auto
hoelzl@29805
  1616
    from exp_boundaries'[OF this] show ?thesis .
hoelzl@29805
  1617
  next
hoelzl@29805
  1618
    case True hence "-x \<le> 0" unfolding less_float_def le_float_def by auto
hoelzl@31809
  1619
hoelzl@40881
  1620
    have "lb_exp prec x \<le> exp x"
hoelzl@29805
  1621
    proof -
hoelzl@29805
  1622
      from exp_boundaries'[OF `-x \<le> 0`]
hoelzl@40881
  1623
      have ub_exp: "exp (- real x) \<le> ub_exp prec (-x)" unfolding atLeastAtMost_iff real_of_float_minus by auto
hoelzl@40881
  1624
hoelzl@40881
  1625
      have "float_divl prec 1 (ub_exp prec (-x)) \<le> 1 / ub_exp prec (-x)" using float_divl[where x=1] by auto
hoelzl@40881
  1626
      also have "\<dots> \<le> exp x"
wenzelm@32960
  1627
        using ub_exp[unfolded inverse_le_iff_le[OF order_less_le_trans[OF exp_gt_zero ub_exp] exp_gt_zero, symmetric]]
wenzelm@32960
  1628
        unfolding exp_minus nonzero_inverse_inverse_eq[OF exp_not_eq_zero] inverse_eq_divide by auto
hoelzl@29805
  1629
      finally show ?thesis unfolding lb_exp.simps if_P[OF True] .
hoelzl@29805
  1630
    qed
hoelzl@29805
  1631
    moreover
hoelzl@40881
  1632
    have "exp x \<le> ub_exp prec x"
hoelzl@29805
  1633
    proof -
hoelzl@29805
  1634
      have "\<not> 0 < -x" using `0 < x` unfolding less_float_def by auto
hoelzl@31809
  1635
hoelzl@29805
  1636
      from exp_boundaries'[OF `-x \<le> 0`]
hoelzl@40881
  1637
      have lb_exp: "lb_exp prec (-x) \<le> exp (- real x)" unfolding atLeastAtMost_iff real_of_float_minus by auto
hoelzl@40881
  1638
hoelzl@40881
  1639
      have "exp x \<le> (1 :: float) / lb_exp prec (-x)"
wenzelm@32960
  1640
        using lb_exp[unfolded inverse_le_iff_le[OF exp_gt_zero lb_exp_pos[OF `\<not> 0 < -x`, unfolded less_float_def real_of_float_0],
wenzelm@32960
  1641
                                                symmetric]]
wenzelm@32960
  1642
        unfolding exp_minus nonzero_inverse_inverse_eq[OF exp_not_eq_zero] inverse_eq_divide real_of_float_1 by auto
hoelzl@40881
  1643
      also have "\<dots> \<le> float_divr prec 1 (lb_exp prec (-x))" using float_divr .
hoelzl@29805
  1644
      finally show ?thesis unfolding ub_exp.simps if_P[OF True] .
hoelzl@29805
  1645
    qed
hoelzl@29805
  1646
    ultimately show ?thesis by auto
hoelzl@29805
  1647
  qed
hoelzl@29805
  1648
qed
hoelzl@29805
  1649
hoelzl@40881
  1650
lemma bnds_exp: "\<forall> (x::real) lx ux. (l, u) = (lb_exp prec lx, ub_exp prec ux) \<and> x \<in> {lx .. ux} \<longrightarrow> l \<le> exp x \<and> exp x \<le> u"
hoelzl@29805
  1651
proof (rule allI, rule allI, rule allI, rule impI)
hoelzl@40881
  1652
  fix x::real and lx ux
hoelzl@40881
  1653
  assume "(l, u) = (lb_exp prec lx, ub_exp prec ux) \<and> x \<in> {lx .. ux}"
hoelzl@40881
  1654
  hence l: "lb_exp prec lx = l " and u: "ub_exp prec ux = u" and x: "x \<in> {lx .. ux}" by auto
hoelzl@29805
  1655
hoelzl@29805
  1656
  { from exp_boundaries[of lx prec, unfolded l]
hoelzl@40881
  1657
    have "l \<le> exp lx" by (auto simp del: lb_exp.simps)
hoelzl@29805
  1658
    also have "\<dots> \<le> exp x" using x by auto
hoelzl@40881
  1659
    finally have "l \<le> exp x" .
hoelzl@29805
  1660
  } moreover
hoelzl@40881
  1661
  { have "exp x \<le> exp ux" using x by auto
hoelzl@40881
  1662
    also have "\<dots> \<le> u" using exp_boundaries[of ux prec, unfolded u] by (auto simp del: ub_exp.simps)
hoelzl@40881
  1663
    finally have "exp x \<le> u" .
hoelzl@40881
  1664
  } ultimately show "l \<le> exp x \<and> exp x \<le> u" ..
hoelzl@29805
  1665
qed
hoelzl@29805
  1666
hoelzl@29805
  1667
section "Logarithm"
hoelzl@29805
  1668
hoelzl@29805
  1669
subsection "Compute the logarithm series"
hoelzl@29805
  1670
hoelzl@31809
  1671
fun ub_ln_horner :: "nat \<Rightarrow> nat \<Rightarrow> nat \<Rightarrow> float \<Rightarrow> float"
hoelzl@29805
  1672
and lb_ln_horner :: "nat \<Rightarrow> nat \<Rightarrow> nat \<Rightarrow> float \<Rightarrow> float" where
hoelzl@29805
  1673
"ub_ln_horner prec 0 i x       = 0" |
hoelzl@29805
  1674
"ub_ln_horner prec (Suc n) i x = rapprox_rat prec 1 (int i) - x * lb_ln_horner prec n (Suc i) x" |
hoelzl@29805
  1675
"lb_ln_horner prec 0 i x       = 0" |
hoelzl@29805
  1676
"lb_ln_horner prec (Suc n) i x = lapprox_rat prec 1 (int i) - x * ub_ln_horner prec n (Suc i) x"
hoelzl@29805
  1677
hoelzl@29805
  1678
lemma ln_bounds:
hoelzl@29805
  1679
  assumes "0 \<le> x" and "x < 1"
haftmann@30952
  1680
  shows "(\<Sum>i=0..<2*n. -1^i * (1 / real (i + 1)) * x ^ (Suc i)) \<le> ln (x + 1)" (is "?lb")
haftmann@30952
  1681
  and "ln (x + 1) \<le> (\<Sum>i=0..<2*n + 1. -1^i * (1 / real (i + 1)) * x ^ (Suc i))" (is "?ub")
hoelzl@29805
  1682
proof -
haftmann@30952
  1683
  let "?a n" = "(1/real (n +1)) * x ^ (Suc n)"
hoelzl@29805
  1684
hoelzl@29805
  1685
  have ln_eq: "(\<Sum> i. -1^i * ?a i) = ln (x + 1)"
hoelzl@29805
  1686
    using ln_series[of "x + 1"] `0 \<le> x` `x < 1` by auto
hoelzl@29805
  1687
hoelzl@29805
  1688
  have "norm x < 1" using assms by auto
hoelzl@31809
  1689
  have "?a ----> 0" unfolding Suc_eq_plus1[symmetric] inverse_eq_divide[symmetric]
hoelzl@29805
  1690
    using LIMSEQ_mult[OF LIMSEQ_inverse_real_of_nat LIMSEQ_Suc[OF LIMSEQ_power_zero[OF `norm x < 1`]]] by auto
hoelzl@29805
  1691
  { fix n have "0 \<le> ?a n" by (rule mult_nonneg_nonneg, auto intro!: mult_nonneg_nonneg simp add: `0 \<le> x`) }
hoelzl@29805
  1692
  { fix n have "?a (Suc n) \<le> ?a n" unfolding inverse_eq_divide[symmetric]
hoelzl@29805
  1693
    proof (rule mult_mono)
hoelzl@29805
  1694
      show "0 \<le> x ^ Suc (Suc n)" by (auto intro!: mult_nonneg_nonneg simp add: `0 \<le> x`)
huffman@36778
  1695
      have "x ^ Suc (Suc n) \<le> x ^ Suc n * 1" unfolding power_Suc2 mult_assoc[symmetric]
wenzelm@32960
  1696
        by (rule mult_left_mono, fact less_imp_le[OF `x < 1`], auto intro!: mult_nonneg_nonneg simp add: `0 \<le> x`)
hoelzl@29805
  1697
      thus "x ^ Suc (Suc n) \<le> x ^ Suc n" by auto
hoelzl@29805
  1698
    qed auto }
hoelzl@29805
  1699
  from summable_Leibniz'(2,4)[OF `?a ----> 0` `\<And>n. 0 \<le> ?a n`, OF `\<And>n. ?a (Suc n) \<le> ?a n`, unfolded ln_eq]
hoelzl@29805
  1700
  show "?lb" and "?ub" by auto
hoelzl@29805
  1701
qed
hoelzl@29805
  1702
hoelzl@31809
  1703
lemma ln_float_bounds:
hoelzl@31098
  1704
  assumes "0 \<le> real x" and "real x < 1"
hoelzl@40881
  1705
  shows "x * lb_ln_horner prec (get_even n) 1 x \<le> ln (x + 1)" (is "?lb \<le> ?ln")
hoelzl@40881
  1706
  and "ln (x + 1) \<le> x * ub_ln_horner prec (get_odd n) 1 x" (is "?ln \<le> ?ub")
hoelzl@29805
  1707
proof -
hoelzl@29805
  1708
  obtain ev where ev: "get_even n = 2 * ev" using get_even_double ..
hoelzl@29805
  1709
  obtain od where od: "get_odd n = 2 * od + 1" using get_odd_double ..
hoelzl@29805
  1710
hoelzl@31098
  1711
  let "?s n" = "-1^n * (1 / real (1 + n)) * (real x)^(Suc n)"
hoelzl@29805
  1712
huffman@36778
  1713
  have "?lb \<le> setsum ?s {0 ..< 2 * ev}" unfolding power_Suc2 mult_assoc[symmetric] real_of_float_mult setsum_left_distrib[symmetric] unfolding mult_commute[of "real x"] ev
hoelzl@29805
  1714
    using horner_bounds(1)[where G="\<lambda> i k. Suc k" and F="\<lambda>x. x" and f="\<lambda>x. x" and lb="\<lambda>n i k x. lb_ln_horner prec n k x" and ub="\<lambda>n i k x. ub_ln_horner prec n k x" and j'=1 and n="2*ev",
hoelzl@31098
  1715
      OF `0 \<le> real x` refl lb_ln_horner.simps ub_ln_horner.simps] `0 \<le> real x`
hoelzl@29805
  1716
    by (rule mult_right_mono)
hoelzl@31098
  1717
  also have "\<dots> \<le> ?ln" using ln_bounds(1)[OF `0 \<le> real x` `real x < 1`] by auto
hoelzl@31809
  1718
  finally show "?lb \<le> ?ln" .
hoelzl@29805
  1719
hoelzl@31098
  1720
  have "?ln \<le> setsum ?s {0 ..< 2 * od + 1}" using ln_bounds(2)[OF `0 \<le> real x` `real x < 1`] by auto
huffman@36778
  1721
  also have "\<dots> \<le> ?ub" unfolding power_Suc2 mult_assoc[symmetric] real_of_float_mult setsum_left_distrib[symmetric] unfolding mult_commute[of "real x"] od
hoelzl@29805
  1722
    using horner_bounds(2)[where G="\<lambda> i k. Suc k" and F="\<lambda>x. x" and f="\<lambda>x. x" and lb="\<lambda>n i k x. lb_ln_horner prec n k x" and ub="\<lambda>n i k x. ub_ln_horner prec n k x" and j'=1 and n="2*od+1",
hoelzl@31098
  1723
      OF `0 \<le> real x` refl lb_ln_horner.simps ub_ln_horner.simps] `0 \<le> real x`
hoelzl@29805
  1724
    by (rule mult_right_mono)
hoelzl@31809
  1725
  finally show "?ln \<le> ?ub" .
hoelzl@29805
  1726
qed
hoelzl@29805
  1727
hoelzl@29805
  1728
lemma ln_add: assumes "0 < x" and "0 < y" shows "ln (x + y) = ln x + ln (1 + y / x)"
hoelzl@29805
  1729
proof -
hoelzl@29805
  1730
  have "x \<noteq> 0" using assms by auto
hoelzl@29805
  1731
  have "x + y = x * (1 + y / x)" unfolding right_distrib times_divide_eq_right nonzero_mult_divide_cancel_left[OF `x \<noteq> 0`] by auto
hoelzl@31809
  1732
  moreover
hoelzl@29805
  1733
  have "0 < y / x" using assms divide_pos_pos by auto
hoelzl@29805
  1734
  hence "0 < 1 + y / x" by auto
hoelzl@29805
  1735
  ultimately show ?thesis using ln_mult assms by auto
hoelzl@29805
  1736
qed
hoelzl@29805
  1737
hoelzl@29805
  1738
subsection "Compute the logarithm of 2"
hoelzl@29805
  1739
hoelzl@31809
  1740
definition ub_ln2 where "ub_ln2 prec = (let third = rapprox_rat (max prec 1) 1 3
hoelzl@31809
  1741
                                        in (Float 1 -1 * ub_ln_horner prec (get_odd prec) 1 (Float 1 -1)) +
hoelzl@29805
  1742
                                           (third * ub_ln_horner prec (get_odd prec) 1 third))"
hoelzl@31809
  1743
definition lb_ln2 where "lb_ln2 prec = (let third = lapprox_rat prec 1 3
hoelzl@31809
  1744
                                        in (Float 1 -1 * lb_ln_horner prec (get_even prec) 1 (Float 1 -1)) +
hoelzl@29805
  1745
                                           (third * lb_ln_horner prec (get_even prec) 1 third))"
hoelzl@29805
  1746
hoelzl@40881
  1747
lemma ub_ln2: "ln 2 \<le> ub_ln2 prec" (is "?ub_ln2")
hoelzl@40881
  1748
  and lb_ln2: "lb_ln2 prec \<le> ln 2" (is "?lb_ln2")
hoelzl@29805
  1749
proof -
hoelzl@29805
  1750
  let ?uthird = "rapprox_rat (max prec 1) 1 3"
hoelzl@29805
  1751
  let ?lthird = "lapprox_rat prec 1 3"
hoelzl@29805
  1752
hoelzl@29805
  1753
  have ln2_sum: "ln 2 = ln (1/2 + 1) + ln (1 / 3 + 1)"
hoelzl@29805
  1754
    using ln_add[of "3 / 2" "1 / 2"] by auto
hoelzl@40881
  1755
  have lb3: "?lthird \<le> 1 / 3" using lapprox_rat[of prec 1 3] by auto
hoelzl@31098
  1756
  hence lb3_ub: "real ?lthird < 1" by auto
hoelzl@31098
  1757
  have lb3_lb: "0 \<le> real ?lthird" using lapprox_rat_bottom[of 1 3] by auto
hoelzl@40881
  1758
  have ub3: "1 / 3 \<le> ?uthird" using rapprox_rat[of 1 3] by auto
hoelzl@31098
  1759
  hence ub3_lb: "0 \<le> real ?uthird" by auto
hoelzl@29805
  1760
hoelzl@31098
  1761
  have lb2: "0 \<le> real (Float 1 -1)" and ub2: "real (Float 1 -1) < 1" unfolding Float_num by auto
hoelzl@29805
  1762
hoelzl@29805
  1763
  have "0 \<le> (1::int)" and "0 < (3::int)" by auto
hoelzl@31098
  1764
  have ub3_ub: "real ?uthird < 1" unfolding rapprox_rat.simps(2)[OF `0 \<le> 1` `0 < 3`]
hoelzl@29805
  1765
    by (rule rapprox_posrat_less1, auto)
hoelzl@29805
  1766
hoelzl@29805
  1767
  have third_gt0: "(0 :: real) < 1 / 3 + 1" by auto
hoelzl@31098
  1768
  have uthird_gt0: "0 < real ?uthird + 1" using ub3_lb by auto
hoelzl@31098
  1769
  have lthird_gt0: "0 < real ?lthird + 1" using lb3_lb by auto
hoelzl@29805
  1770
hoelzl@31098
  1771
  show ?ub_ln2 unfolding ub_ln2_def Let_def real_of_float_add ln2_sum Float_num(4)[symmetric]
hoelzl@29805
  1772
  proof (rule add_mono, fact ln_float_bounds(2)[OF lb2 ub2])
hoelzl@31098
  1773
    have "ln (1 / 3 + 1) \<le> ln (real ?uthird + 1)" unfolding ln_le_cancel_iff[OF third_gt0 uthird_gt0] using ub3 by auto
hoelzl@40881
  1774
    also have "\<dots> \<le> ?uthird * ub_ln_horner prec (get_odd prec) 1 ?uthird"
hoelzl@29805
  1775
      using ln_float_bounds(2)[OF ub3_lb ub3_ub] .
hoelzl@40881
  1776
    finally show "ln (1 / 3 + 1) \<le> ?uthird * ub_ln_horner prec (get_odd prec) 1 ?uthird" .
hoelzl@29805
  1777
  qed
hoelzl@31098
  1778
  show ?lb_ln2 unfolding lb_ln2_def Let_def real_of_float_add ln2_sum Float_num(4)[symmetric]
hoelzl@29805
  1779
  proof (rule add_mono, fact ln_float_bounds(1)[OF lb2 ub2])
hoelzl@40881
  1780
    have "?lthird * lb_ln_horner prec (get_even prec) 1 ?lthird \<le> ln (real ?lthird + 1)"
hoelzl@29805
  1781
      using ln_float_bounds(1)[OF lb3_lb lb3_ub] .
hoelzl@29805
  1782
    also have "\<dots> \<le> ln (1 / 3 + 1)" unfolding ln_le_cancel_iff[OF lthird_gt0 third_gt0] using lb3 by auto
hoelzl@40881
  1783
    finally show "?lthird * lb_ln_horner prec (get_even prec) 1 ?lthird \<le> ln (1 / 3 + 1)" .
hoelzl@29805
  1784
  qed
hoelzl@29805
  1785
qed
hoelzl@29805
  1786
hoelzl@29805
  1787
subsection "Compute the logarithm in the entire domain"
hoelzl@29805
  1788
hoelzl@29805
  1789
function ub_ln :: "nat \<Rightarrow> float \<Rightarrow> float option" and lb_ln :: "nat \<Rightarrow> float \<Rightarrow> float option" where
hoelzl@31468
  1790
"ub_ln prec x = (if x \<le> 0          then None
hoelzl@31468
  1791
            else if x < 1          then Some (- the (lb_ln prec (float_divl (max prec 1) 1 x)))
hoelzl@31468
  1792
            else let horner = \<lambda>x. x * ub_ln_horner prec (get_odd prec) 1 x in
hoelzl@31468
  1793
                 if x \<le> Float 3 -1 then Some (horner (x - 1))
hoelzl@31468
  1794
            else if x < Float 1 1  then Some (horner (Float 1 -1) + horner (x * rapprox_rat prec 2 3 - 1))
hoelzl@31468
  1795
                                   else let l = bitlen (mantissa x) - 1 in
hoelzl@31468
  1796
                                        Some (ub_ln2 prec * (Float (scale x + l) 0) + horner (Float (mantissa x) (- l) - 1)))" |
hoelzl@31468
  1797
"lb_ln prec x = (if x \<le> 0          then None
hoelzl@31468
  1798
            else if x < 1          then Some (- the (ub_ln prec (float_divr prec 1 x)))
hoelzl@31468
  1799
            else let horner = \<lambda>x. x * lb_ln_horner prec (get_even prec) 1 x in
hoelzl@31468
  1800
                 if x \<le> Float 3 -1 then Some (horner (x - 1))
hoelzl@31468
  1801
            else if x < Float 1 1  then Some (horner (Float 1 -1) +
hoelzl@31468
  1802
                                              horner (max (x * lapprox_rat prec 2 3 - 1) 0))
hoelzl@31468
  1803
                                   else let l = bitlen (mantissa x) - 1 in
hoelzl@31468
  1804
                                        Some (lb_ln2 prec * (Float (scale x + l) 0) + horner (Float (mantissa x) (- l) - 1)))"
hoelzl@29805
  1805
by pat_completeness auto
hoelzl@29805
  1806
hoelzl@29805
  1807
termination proof (relation "measure (\<lambda> v. let (prec, x) = sum_case id id v in (if x < 1 then 1 else 0))", auto)
hoelzl@29805
  1808
  fix prec x assume "\<not> x \<le> 0" and "x < 1" and "float_divl (max prec (Suc 0)) 1 x < 1"
hoelzl@29805
  1809
  hence "0 < x" and "0 < max prec (Suc 0)" unfolding less_float_def le_float_def by auto
hoelzl@29805
  1810
  from float_divl_pos_less1_bound[OF `0 < x` `x < 1` `0 < max prec (Suc 0)`]
hoelzl@29805
  1811
  show False using `float_divl (max prec (Suc 0)) 1 x < 1` unfolding less_float_def le_float_def by auto
hoelzl@29805
  1812
next
hoelzl@29805
  1813
  fix prec x assume "\<not> x \<le> 0" and "x < 1" and "float_divr prec 1 x < 1"
hoelzl@29805
  1814
  hence "0 < x" unfolding less_float_def le_float_def by auto
hoelzl@29805
  1815
  from float_divr_pos_less1_lower_bound[OF `0 < x` `x < 1`, of prec]
hoelzl@29805
  1816
  show False using `float_divr prec 1 x < 1` unfolding less_float_def le_float_def by auto
hoelzl@29805
  1817
qed
hoelzl@29805
  1818
hoelzl@40881
  1819
lemma ln_shifted_float: assumes "0 < m" shows "ln (Float m e) = ln 2 * (e + (bitlen m - 1)) + ln (Float m (- (bitlen m - 1)))"
hoelzl@29805
  1820
proof -
hoelzl@29805
  1821
  let ?B = "2^nat (bitlen m - 1)"
hoelzl@29805
  1822
  have "0 < real m" and "\<And>X. (0 :: real) < 2^X" and "0 < (2 :: real)" and "m \<noteq> 0" using assms by auto
hoelzl@29805
  1823
  hence "0 \<le> bitlen m - 1" using bitlen_ge1[OF `m \<noteq> 0`] by auto
hoelzl@31468
  1824
  show ?thesis
hoelzl@29805
  1825
  proof (cases "0 \<le> e")
hoelzl@29805
  1826
    case True
hoelzl@29805
  1827
    show ?thesis unfolding normalized_float[OF `m \<noteq> 0`]
hoelzl@31468
  1828
      unfolding ln_div[OF `0 < real m` `0 < ?B`] real_of_int_add ln_realpow[OF `0 < 2`]
hoelzl@31468
  1829
      unfolding real_of_float_ge0_exp[OF True] ln_mult[OF `0 < real m` `0 < 2^nat e`]
hoelzl@29805
  1830
      ln_realpow[OF `0 < 2`] algebra_simps using `0 \<le> bitlen m - 1` True by auto
hoelzl@29805
  1831
  next
hoelzl@29805
  1832
    case False hence "0 < -e" by auto
hoelzl@29805
  1833
    hence pow_gt0: "(0::real) < 2^nat (-e)" by auto
hoelzl@29805
  1834
    hence inv_gt0: "(0::real) < inverse (2^nat (-e))" by auto
hoelzl@29805
  1835
    show ?thesis unfolding normalized_float[OF `m \<noteq> 0`]
hoelzl@31468
  1836
      unfolding ln_div[OF `0 < real m` `0 < ?B`] real_of_int_add ln_realpow[OF `0 < 2`]
hoelzl@31098
  1837
      unfolding real_of_float_nge0_exp[OF False] ln_mult[OF `0 < real m` inv_gt0] ln_inverse[OF pow_gt0]
hoelzl@29805
  1838
      ln_realpow[OF `0 < 2`] algebra_simps using `0 \<le> bitlen m - 1` False by auto
hoelzl@29805
  1839
  qed
hoelzl@29805
  1840
qed
hoelzl@29805
  1841
hoelzl@29805
  1842
lemma ub_ln_lb_ln_bounds': assumes "1 \<le> x"
hoelzl@40881
  1843
  shows "the (lb_ln prec x) \<le> ln x \<and> ln x \<le> the (ub_ln prec x)"
hoelzl@29805
  1844
  (is "?lb \<le> ?ln \<and> ?ln \<le> ?ub")
hoelzl@29805
  1845
proof (cases "x < Float 1 1")
hoelzl@31468
  1846
  case True
hoelzl@31468
  1847
  hence "real (x - 1) < 1" and "real x < 2" unfolding less_float_def Float_num by auto
hoelzl@29805
  1848
  have "\<not> x \<le> 0" and "\<not> x < 1" using `1 \<le> x` unfolding less_float_def le_float_def by auto
hoelzl@31098
  1849
  hence "0 \<le> real (x - 1)" using `1 \<le> x` unfolding less_float_def Float_num by auto
hoelzl@31468
  1850
hoelzl@40881
  1851
  have [simp]: "(Float 3 -1) = 3 / 2" by (simp add: real_of_float_def pow2_def)
hoelzl@31468
  1852
hoelzl@31468
  1853
  show ?thesis
hoelzl@31468
  1854
  proof (cases "x \<le> Float 3 -1")
hoelzl@31468
  1855
    case True
hoelzl@31468
  1856
    show ?thesis unfolding lb_ln.simps unfolding ub_ln.simps Let_def
hoelzl@31468
  1857
      using ln_float_bounds[OF `0 \<le> real (x - 1)` `real (x - 1) < 1`, of prec] `\<not> x \<le> 0` `\<not> x < 1` True
hoelzl@31468
  1858
      by auto
hoelzl@31468
  1859
  next
hoelzl@40881
  1860
    case False hence *: "3 / 2 < x" by (auto simp add: le_float_def)
hoelzl@40881
  1861
hoelzl@40881
  1862
    with ln_add[of "3 / 2" "x - 3 / 2"]
hoelzl@40881
  1863
    have add: "ln x = ln (3 / 2) + ln (real x * 2 / 3)"
hoelzl@31468
  1864
      by (auto simp add: algebra_simps diff_divide_distrib)
hoelzl@31468
  1865
hoelzl@31468
  1866
    let "?ub_horner x" = "x * ub_ln_horner prec (get_odd prec) 1 x"
hoelzl@31468
  1867
    let "?lb_horner x" = "x * lb_ln_horner prec (get_even prec) 1 x"
hoelzl@31468
  1868
hoelzl@31468
  1869
    { have up: "real (rapprox_rat prec 2 3) \<le> 1"
wenzelm@32960
  1870
        by (rule rapprox_rat_le1) simp_all
hoelzl@40881
  1871
      have low: "2 / 3 \<le> rapprox_rat prec 2 3"
wenzelm@32960
  1872
        by (rule order_trans[OF _ rapprox_rat]) simp
hoelzl@31468
  1873
      from mult_less_le_imp_less[OF * low] *
hoelzl@31468
  1874
      have pos: "0 < real (x * rapprox_rat prec 2 3 - 1)" by auto
hoelzl@31468
  1875
hoelzl@31468
  1876
      have "ln (real x * 2/3)
wenzelm@32960
  1877
        \<le> ln (real (x * rapprox_rat prec 2 3 - 1) + 1)"
hoelzl@31468
  1878
      proof (rule ln_le_cancel_iff[symmetric, THEN iffD1])
wenzelm@32960
  1879
        show "real x * 2 / 3 \<le> real (x * rapprox_rat prec 2 3 - 1) + 1"
wenzelm@32960
  1880
          using * low by auto
wenzelm@32960
  1881
        show "0 < real x * 2 / 3" using * by simp
wenzelm@32960
  1882
        show "0 < real (x * rapprox_rat prec 2 3 - 1) + 1" using pos by auto
hoelzl@31468
  1883
      qed
hoelzl@40881
  1884
      also have "\<dots> \<le> ?ub_horner (x * rapprox_rat prec 2 3 - 1)"
hoelzl@31468
  1885
      proof (rule ln_float_bounds(2))
wenzelm@32960
  1886
        from mult_less_le_imp_less[OF `real x < 2` up] low *
wenzelm@32960
  1887
        show "real (x * rapprox_rat prec 2 3 - 1) < 1" by auto
wenzelm@32960
  1888
        show "0 \<le> real (x * rapprox_rat prec 2 3 - 1)" using pos by auto
hoelzl@31468
  1889
      qed
hoelzl@40881
  1890
      finally have "ln x
hoelzl@40881
  1891
        \<le> ?ub_horner (Float 1 -1)
hoelzl@40881
  1892
          + ?ub_horner (x * rapprox_rat prec 2 3 - 1)"
wenzelm@32960
  1893
        using ln_float_bounds(2)[of "Float 1 -1" prec prec] add by auto }
hoelzl@31468
  1894
    moreover
hoelzl@31468
  1895
    { let ?max = "max (x * lapprox_rat prec 2 3 - 1) 0"
hoelzl@31468
  1896
hoelzl@40881
  1897
      have up: "lapprox_rat prec 2 3 \<le> 2/3"
wenzelm@32960
  1898
        by (rule order_trans[OF lapprox_rat], simp)
hoelzl@31468
  1899
hoelzl@31468
  1900
      have low: "0 \<le> real (lapprox_rat prec 2 3)"
wenzelm@32960
  1901
        using lapprox_rat_bottom[of 2 3 prec] by simp
hoelzl@31468
  1902
hoelzl@40881
  1903
      have "?lb_horner ?max
wenzelm@32960
  1904
        \<le> ln (real ?max + 1)"
hoelzl@31468
  1905
      proof (rule ln_float_bounds(1))
wenzelm@32960
  1906
        from mult_less_le_imp_less[OF `real x < 2` up] * low
wenzelm@32960
  1907
        show "real ?max < 1" by (cases "real (lapprox_rat prec 2 3) = 0",
wenzelm@32960
  1908
          auto simp add: real_of_float_max)
wenzelm@32960
  1909
        show "0 \<le> real ?max" by (auto simp add: real_of_float_max)
hoelzl@31468
  1910
      qed
hoelzl@31468
  1911
      also have "\<dots> \<le> ln (real x * 2/3)"
hoelzl@31468
  1912
      proof (rule ln_le_cancel_iff[symmetric, THEN iffD1])
wenzelm@32960
  1913
        show "0 < real ?max + 1" by (auto simp add: real_of_float_max)
wenzelm@32960
  1914
        show "0 < real x * 2/3" using * by auto
wenzelm@32960
  1915
        show "real ?max + 1 \<le> real x * 2/3" using * up
wenzelm@32960
  1916
          by (cases "0 < real x * real (lapprox_posrat prec 2 3) - 1",
wenzelm@32960
  1917
              auto simp add: real_of_float_max min_max.sup_absorb1)
hoelzl@31468
  1918
      qed
hoelzl@40881
  1919
      finally have "?lb_horner (Float 1 -1) + ?lb_horner ?max
hoelzl@40881
  1920
        \<le> ln x"
wenzelm@32960
  1921
        using ln_float_bounds(1)[of "Float 1 -1" prec prec] add by auto }
hoelzl@31468
  1922
    ultimately
hoelzl@31468
  1923
    show ?thesis unfolding lb_ln.simps unfolding ub_ln.simps Let_def
hoelzl@31468
  1924
      using `\<not> x \<le> 0` `\<not> x < 1` True False by auto
hoelzl@31468
  1925
  qed
hoelzl@29805
  1926
next
hoelzl@29805
  1927
  case False
hoelzl@31468
  1928
  hence "\<not> x \<le> 0" and "\<not> x < 1" "0 < x" "\<not> x \<le> Float 3 -1"
hoelzl@31468
  1929
    using `1 \<le> x` unfolding less_float_def le_float_def real_of_float_simp pow2_def
hoelzl@31468
  1930
    by auto
hoelzl@29805
  1931
  show ?thesis
hoelzl@29805
  1932
  proof (cases x)
hoelzl@29805
  1933
    case (Float m e)
hoelzl@29805
  1934
    let ?s = "Float (e + (bitlen m - 1)) 0"
hoelzl@29805
  1935
    let ?x = "Float m (- (bitlen m - 1))"
hoelzl@29805
  1936
hoelzl@29805
  1937
    have "0 < m" and "m \<noteq> 0" using float_pos_m_pos `0 < x` Float by auto
hoelzl@29805
  1938
hoelzl@29805
  1939
    {
hoelzl@40881
  1940
      have "lb_ln2 prec * ?s \<le> ln 2 * (e + (bitlen m - 1))" (is "?lb2 \<le> _")
wenzelm@32960
  1941
        unfolding real_of_float_mult real_of_float_ge0_exp[OF order_refl] nat_0 power_0 mult_1_right
wenzelm@32960
  1942
        using lb_ln2[of prec]
hoelzl@29805
  1943
      proof (rule mult_right_mono)
wenzelm@32960
  1944
        have "1 \<le> Float m e" using `1 \<le> x` Float unfolding le_float_def by auto
wenzelm@32960
  1945
        from float_gt1_scale[OF this]
wenzelm@32960
  1946
        show "0 \<le> real (e + (bitlen m - 1))" by auto
hoelzl@29805
  1947
      qed
hoelzl@29805
  1948
      moreover
hoelzl@29805
  1949
      from bitlen_div[OF `0 < m`, unfolded normalized_float[OF `m \<noteq> 0`, symmetric]]
hoelzl@31098
  1950
      have "0 \<le> real (?x - 1)" and "real (?x - 1) < 1" by auto
hoelzl@29805
  1951
      from ln_float_bounds(1)[OF this]
hoelzl@40881
  1952
      have "(?x - 1) * lb_ln_horner prec (get_even prec) 1 (?x - 1) \<le> ln ?x" (is "?lb_horner \<le> _") by auto
hoelzl@40881
  1953
      ultimately have "?lb2 + ?lb_horner \<le> ln x"
wenzelm@32960
  1954
        unfolding Float ln_shifted_float[OF `0 < m`, of e] by auto
hoelzl@31468
  1955
    }
hoelzl@29805
  1956
    moreover
hoelzl@29805
  1957
    {
hoelzl@29805
  1958
      from bitlen_div[OF `0 < m`, unfolded normalized_float[OF `m \<noteq> 0`, symmetric]]
hoelzl@31098
  1959
      have "0 \<le> real (?x - 1)" and "real (?x - 1) < 1" by auto
hoelzl@29805
  1960
      from ln_float_bounds(2)[OF this]
hoelzl@40881
  1961
      have "ln ?x \<le> (?x - 1) * ub_ln_horner prec (get_odd prec) 1 (?x - 1)" (is "_ \<le> ?ub_horner") by auto
hoelzl@29805
  1962
      moreover
hoelzl@40881
  1963
      have "ln 2 * (e + (bitlen m - 1)) \<le> ub_ln2 prec * ?s" (is "_ \<le> ?ub2")
wenzelm@32960
  1964
        unfolding real_of_float_mult real_of_float_ge0_exp[OF order_refl] nat_0 power_0 mult_1_right
wenzelm@32960
  1965
        using ub_ln2[of prec]
hoelzl@29805
  1966
      proof (rule mult_right_mono)
wenzelm@32960
  1967
        have "1 \<le> Float m e" using `1 \<le> x` Float unfolding le_float_def by auto
wenzelm@32960
  1968
        from float_gt1_scale[OF this]
wenzelm@32960
  1969
        show "0 \<le> real (e + (bitlen m - 1))" by auto
hoelzl@29805
  1970
      qed
hoelzl@40881
  1971
      ultimately have "ln x \<le> ?ub2 + ?ub_horner"
wenzelm@32960
  1972
        unfolding Float ln_shifted_float[OF `0 < m`, of e] by auto
hoelzl@29805
  1973
    }
hoelzl@29805
  1974
    ultimately show ?thesis unfolding lb_ln.simps unfolding ub_ln.simps
hoelzl@31468
  1975
      unfolding if_not_P[OF `\<not> x \<le> 0`] if_not_P[OF `\<not> x < 1`] if_not_P[OF False] if_not_P[OF `\<not> x \<le> Float 3 -1`] Let_def
hoelzl@31468
  1976
      unfolding scale.simps[of m e, unfolded Float[symmetric]] mantissa.simps[of m e, unfolded Float[symmetric]] real_of_float_add
hoelzl@31468
  1977
      by auto
hoelzl@29805
  1978
  qed
hoelzl@29805
  1979
qed
hoelzl@29805
  1980
hoelzl@29805
  1981
lemma ub_ln_lb_ln_bounds: assumes "0 < x"
hoelzl@40881
  1982
  shows "the (lb_ln prec x) \<le> ln x \<and> ln x \<le> the (ub_ln prec x)"
hoelzl@29805
  1983
  (is "?lb \<le> ?ln \<and> ?ln \<le> ?ub")
hoelzl@29805
  1984
proof (cases "x < 1")
hoelzl@29805
  1985
  case False hence "1 \<le> x" unfolding less_float_def le_float_def by auto
hoelzl@29805
  1986
  show ?thesis using ub_ln_lb_ln_bounds'[OF `1 \<le> x`] .
hoelzl@29805
  1987
next
hoelzl@29805
  1988
  case True have "\<not> x \<le> 0" using `0 < x` unfolding less_float_def le_float_def by auto
hoelzl@29805
  1989
hoelzl@31098
  1990
  have "0 < real x" and "real x \<noteq> 0" using `0 < x` unfolding less_float_def by auto
hoelzl@31098
  1991
  hence A: "0 < 1 / real x" by auto
hoelzl@29805
  1992
hoelzl@29805
  1993
  {
hoelzl@29805
  1994
    let ?divl = "float_divl (max prec 1) 1 x"
hoelzl@29805
  1995
    have A': "1 \<le> ?divl" using float_divl_pos_less1_bound[OF `0 < x` `x < 1`] unfolding le_float_def less_float_def by auto
hoelzl@31098
  1996
    hence B: "0 < real ?divl" unfolding le_float_def by auto
hoelzl@31468
  1997
hoelzl@40881
  1998
    have "ln ?divl \<le> ln (1 / x)" unfolding ln_le_cancel_iff[OF B A] using float_divl[of _ 1 x] by auto
hoelzl@40881
  1999
    hence "ln x \<le> - ln ?divl" unfolding nonzero_inverse_eq_divide[OF `real x \<noteq> 0`, symmetric] ln_inverse[OF `0 < real x`] by auto
hoelzl@31468
  2000
    from this ub_ln_lb_ln_bounds'[OF A', THEN conjunct1, THEN le_imp_neg_le]
hoelzl@40881
  2001
    have "?ln \<le> - the (lb_ln prec ?divl)" unfolding real_of_float_minus by (rule order_trans)
hoelzl@29805
  2002
  } moreover
hoelzl@29805
  2003
  {
hoelzl@29805
  2004
    let ?divr = "float_divr prec 1 x"
hoelzl@29805
  2005
    have A': "1 \<le> ?divr" using float_divr_pos_less1_lower_bound[OF `0 < x` `x < 1`] unfolding le_float_def less_float_def by auto
hoelzl@31098
  2006
    hence B: "0 < real ?divr" unfolding le_float_def by auto
hoelzl@31468
  2007
hoelzl@40881
  2008
    have "ln (1 / x) \<le> ln ?divr" unfolding ln_le_cancel_iff[OF A B] using float_divr[of 1 x] by auto
hoelzl@40881
  2009
    hence "- ln ?divr \<le> ln x" unfolding nonzero_inverse_eq_divide[OF `real x \<noteq> 0`, symmetric] ln_inverse[OF `0 < real x`] by auto
hoelzl@29805
  2010
    from ub_ln_lb_ln_bounds'[OF A', THEN conjunct2, THEN le_imp_neg_le] this
hoelzl@40881
  2011
    have "- the (ub_ln prec ?divr) \<le> ?ln" unfolding real_of_float_minus by (rule order_trans)
hoelzl@29805
  2012
  }
hoelzl@29805
  2013
  ultimately show ?thesis unfolding lb_ln.simps[where x=x]  ub_ln.simps[where x=x]
hoelzl@29805
  2014
    unfolding if_not_P[OF `\<not> x \<le> 0`] if_P[OF True] by auto
hoelzl@29805
  2015
qed
hoelzl@29805
  2016
hoelzl@29805
  2017
lemma lb_ln: assumes "Some y = lb_ln prec x"
hoelzl@40881
  2018
  shows "y \<le> ln x" and "0 < real x"
hoelzl@29805
  2019
proof -
hoelzl@29805
  2020
  have "0 < x"
hoelzl@29805
  2021
  proof (rule ccontr)
hoelzl@29805
  2022
    assume "\<not> 0 < x" hence "x \<le> 0" unfolding le_float_def less_float_def by auto
hoelzl@29805
  2023
    thus False using assms by auto
hoelzl@29805
  2024
  qed
hoelzl@31098
  2025
  thus "0 < real x" unfolding less_float_def by auto
hoelzl@40881
  2026
  have "the (lb_ln prec x) \<le> ln x" using ub_ln_lb_ln_bounds[OF `0 < x`] ..
hoelzl@40881
  2027
  thus "y \<le> ln x" unfolding assms[symmetric] by auto
hoelzl@29805
  2028
qed
hoelzl@29805
  2029
hoelzl@29805
  2030
lemma ub_ln: assumes "Some y = ub_ln prec x"
hoelzl@40881
  2031
  shows "ln x \<le> y" and "0 < real x"
hoelzl@29805
  2032
proof -
hoelzl@29805
  2033
  have "0 < x"
hoelzl@29805
  2034
  proof (rule ccontr)
hoelzl@29805
  2035
    assume "\<not> 0 < x" hence "x \<le> 0" unfolding le_float_def less_float_def by auto
hoelzl@29805
  2036
    thus False using assms by auto
hoelzl@29805
  2037
  qed
hoelzl@31098
  2038
  thus "0 < real x" unfolding less_float_def by auto
hoelzl@40881
  2039
  have "ln x \<le> the (ub_ln prec x)" using ub_ln_lb_ln_bounds[OF `0 < x`] ..
hoelzl@40881
  2040
  thus "ln x \<le> y" unfolding assms[symmetric] by auto
hoelzl@29805
  2041
qed
hoelzl@29805
  2042
hoelzl@40881
  2043
lemma bnds_ln: "\<forall> (x::real) lx ux. (Some l, Some u) = (lb_ln prec lx, ub_ln prec ux) \<and> x \<in> {lx .. ux} \<longrightarrow> l \<le> ln x \<and> ln x \<le> u"
hoelzl@29805
  2044
proof (rule allI, rule allI, rule allI, rule impI)
hoelzl@40881
  2045
  fix x::real and lx ux
hoelzl@40881
  2046
  assume "(Some l, Some u) = (lb_ln prec lx, ub_ln prec ux) \<and> x \<in> {lx .. ux}"
hoelzl@40881
  2047
  hence l: "Some l = lb_ln prec lx " and u: "Some u = ub_ln prec ux" and x: "x \<in> {lx .. ux}" by auto
hoelzl@40881
  2048
hoelzl@40881
  2049
  have "ln ux \<le> u" and "0 < real ux" using ub_ln u by auto
hoelzl@40881
  2050
  have "l \<le> ln lx" and "0 < real lx" and "0 < x" using lb_ln[OF l] x by auto
hoelzl@40881
  2051
hoelzl@40881
  2052
  from ln_le_cancel_iff[OF `0 < real lx` `0 < x`] `l \<le> ln lx`
hoelzl@40881
  2053
  have "l \<le> ln x" using x unfolding atLeastAtMost_iff by auto
hoelzl@29805
  2054
  moreover
hoelzl@40881
  2055
  from ln_le_cancel_iff[OF `0 < x` `0 < real ux`] `ln ux \<le> real u`
hoelzl@40881
  2056
  have "ln x \<le> u" using x unfolding atLeastAtMost_iff by auto
hoelzl@40881
  2057
  ultimately show "l \<le> ln x \<and> ln x \<le> u" ..
hoelzl@29805
  2058
qed
hoelzl@29805
  2059
hoelzl@29805
  2060
section "Implement floatarith"
hoelzl@29805
  2061
hoelzl@29805
  2062
subsection "Define syntax and semantics"
hoelzl@29805
  2063
hoelzl@29805
  2064
datatype floatarith
hoelzl@29805
  2065
  = Add floatarith floatarith
hoelzl@29805
  2066
  | Minus floatarith
hoelzl@29805
  2067
  | Mult floatarith floatarith
hoelzl@29805
  2068
  | Inverse floatarith
hoelzl@29805
  2069
  | Cos floatarith
hoelzl@29805
  2070
  | Arctan floatarith
hoelzl@29805
  2071
  | Abs floatarith
hoelzl@29805
  2072
  | Max floatarith floatarith
hoelzl@29805
  2073
  | Min floatarith floatarith
hoelzl@29805
  2074
  | Pi
hoelzl@29805
  2075
  | Sqrt floatarith
hoelzl@29805
  2076
  | Exp floatarith
hoelzl@29805
  2077
  | Ln floatarith
hoelzl@29805
  2078
  | Power floatarith nat
hoelzl@32919
  2079
  | Var nat
hoelzl@29805
  2080
  | Num float
hoelzl@29805
  2081
hoelzl@31863
  2082
fun interpret_floatarith :: "floatarith \<Rightarrow> real list \<Rightarrow> real" where
hoelzl@31098
  2083
"interpret_floatarith (Add a b) vs   = (interpret_floatarith a vs) + (interpret_floatarith b vs)" |
hoelzl@31098
  2084
"interpret_floatarith (Minus a) vs    = - (interpret_floatarith a vs)" |
hoelzl@31098
  2085
"interpret_floatarith (Mult a b) vs   = (interpret_floatarith a vs) * (interpret_floatarith b vs)" |
hoelzl@31098
  2086
"interpret_floatarith (Inverse a) vs  = inverse (interpret_floatarith a vs)" |
hoelzl@31098
  2087
"interpret_floatarith (Cos a) vs      = cos (interpret_floatarith a vs)" |
hoelzl@31098
  2088
"interpret_floatarith (Arctan a) vs   = arctan (interpret_floatarith a vs)" |
hoelzl@31098
  2089
"interpret_floatarith (Min a b) vs    = min (interpret_floatarith a vs) (interpret_floatarith b vs)" |
hoelzl@31098
  2090
"interpret_floatarith (Max a b) vs    = max (interpret_floatarith a vs) (interpret_floatarith b vs)" |
hoelzl@31098
  2091
"interpret_floatarith (Abs a) vs      = abs (interpret_floatarith a vs)" |
hoelzl@31098
  2092
"interpret_floatarith Pi vs           = pi" |
hoelzl@31098
  2093
"interpret_floatarith (Sqrt a) vs     = sqrt (interpret_floatarith a vs)" |
hoelzl@31098
  2094
"interpret_floatarith (Exp a) vs      = exp (interpret_floatarith a vs)" |
hoelzl@31098
  2095
"interpret_floatarith (Ln a) vs       = ln (interpret_floatarith a vs)" |
hoelzl@31098
  2096
"interpret_floatarith (Power a n) vs  = (interpret_floatarith a vs)^n" |
hoelzl@40881
  2097
"interpret_floatarith (Num f) vs      = f" |
hoelzl@32919
  2098
"interpret_floatarith (Var n) vs     = vs ! n"
hoelzl@29805
  2099
hoelzl@31811
  2100
lemma interpret_floatarith_divide: "interpret_floatarith (Mult a (Inverse b)) vs = (interpret_floatarith a vs) / (interpret_floatarith b vs)"
huffman@36778
  2101
  unfolding divide_inverse interpret_floatarith.simps ..
hoelzl@31811
  2102
hoelzl@31811
  2103
lemma interpret_floatarith_diff: "interpret_floatarith (Add a (Minus b)) vs = (interpret_floatarith a vs) - (interpret_floatarith b vs)"
haftmann@37887
  2104
  unfolding diff_minus interpret_floatarith.simps ..
hoelzl@31811
  2105
hoelzl@31811
  2106
lemma interpret_floatarith_sin: "interpret_floatarith (Cos (Add (Mult Pi (Num (Float 1 -1))) (Minus a))) vs =
hoelzl@31811
  2107
  sin (interpret_floatarith a vs)"
hoelzl@31811
  2108
  unfolding sin_cos_eq interpret_floatarith.simps
haftmann@37887
  2109
            interpret_floatarith_divide interpret_floatarith_diff diff_minus
hoelzl@31811
  2110
  by auto
hoelzl@31811
  2111
hoelzl@31811
  2112
lemma interpret_floatarith_tan:
hoelzl@31811
  2113
  "interpret_floatarith (Mult (Cos (Add (Mult Pi (Num (Float 1 -1))) (Minus a))) (Inverse (Cos a))) vs =
hoelzl@31811
  2114
   tan (interpret_floatarith a vs)"
huffman@36778
  2115
  unfolding interpret_floatarith.simps(3,4) interpret_floatarith_sin tan_def divide_inverse
hoelzl@31811
  2116
  by auto
hoelzl@31811
  2117
hoelzl@31811
  2118
lemma interpret_floatarith_powr: "interpret_floatarith (Exp (Mult b (Ln a))) vs = (interpret_floatarith a vs) powr (interpret_floatarith b vs)"
hoelzl@31811
  2119
  unfolding powr_def interpret_floatarith.simps ..
hoelzl@31811
  2120
hoelzl@31811
  2121
lemma interpret_floatarith_log: "interpret_floatarith ((Mult (Ln x) (Inverse (Ln b)))) vs = log (interpret_floatarith b vs) (interpret_floatarith x vs)"
huffman@36778
  2122
  unfolding log_def interpret_floatarith.simps divide_inverse ..
hoelzl@31811
  2123
hoelzl@31811
  2124
lemma interpret_floatarith_num:
hoelzl@31811
  2125
  shows "interpret_floatarith (Num (Float 0 0)) vs = 0"
hoelzl@31811
  2126
  and "interpret_floatarith (Num (Float 1 0)) vs = 1"
hoelzl@31811
  2127
  and "interpret_floatarith (Num (Float (number_of a) 0)) vs = number_of a" by auto
hoelzl@31811
  2128
hoelzl@29805
  2129
subsection "Implement approximation function"
hoelzl@29805
  2130
hoelzl@29805
  2131
fun lift_bin' :: "(float * float) option \<Rightarrow> (float * float) option \<Rightarrow> (float \<Rightarrow> float \<Rightarrow> float \<Rightarrow> float \<Rightarrow> (float * float)) \<Rightarrow> (float * float) option" where
hoelzl@29805
  2132
"lift_bin' (Some (l1, u1)) (Some (l2, u2)) f = Some (f l1 u1 l2 u2)" |
hoelzl@29805
  2133
"lift_bin' a b f = None"
hoelzl@29805
  2134
hoelzl@29805
  2135
fun lift_un :: "(float * float) option \<Rightarrow> (float \<Rightarrow> float \<Rightarrow> ((float option) * (float option))) \<Rightarrow> (float * float) option" where
hoelzl@29805
  2136
"lift_un (Some (l1, u1)) f = (case (f l1 u1) of (Some l, Some u) \<Rightarrow> Some (l, u)
hoelzl@29805
  2137
                                             | t \<Rightarrow> None)" |
hoelzl@29805
  2138
"lift_un b f = None"
hoelzl@29805
  2139
hoelzl@29805
  2140
fun lift_un' :: "(float * float) option \<Rightarrow> (float \<Rightarrow> float \<Rightarrow> (float * float)) \<Rightarrow> (float * float) option" where
hoelzl@29805
  2141
"lift_un' (Some (l1, u1)) f = Some (f l1 u1)" |
hoelzl@29805
  2142
"lift_un' b f = None"
hoelzl@29805
  2143
hoelzl@31811
  2144
definition
hoelzl@31811
  2145
"bounded_by xs vs \<longleftrightarrow>
hoelzl@31811
  2146
  (\<forall> i < length vs. case vs ! i of None \<Rightarrow> True
hoelzl@31811
  2147
         | Some (l, u) \<Rightarrow> xs ! i \<in> { real l .. real u })"
hoelzl@31811
  2148
hoelzl@31811
  2149
lemma bounded_byE:
hoelzl@31811
  2150
  assumes "bounded_by xs vs"
hoelzl@31811
  2151
  shows "\<And> i. i < length vs \<Longrightarrow> case vs ! i of None \<Rightarrow> True
hoelzl@31811
  2152
         | Some (l, u) \<Rightarrow> xs ! i \<in> { real l .. real u }"
hoelzl@31811
  2153
  using assms bounded_by_def by blast
hoelzl@31811
  2154
hoelzl@31811
  2155
lemma bounded_by_update:
hoelzl@31811
  2156
  assumes "bounded_by xs vs"
hoelzl@31811
  2157
  and bnd: "xs ! i \<in> { real l .. real u }"
hoelzl@31811
  2158
  shows "bounded_by xs (vs[i := Some (l,u)])"
hoelzl@31811
  2159
proof -
hoelzl@31811
  2160
{ fix j
hoelzl@31811
  2161
  let ?vs = "vs[i := Some (l,u)]"
hoelzl@31811
  2162
  assume "j < length ?vs" hence [simp]: "j < length vs" by simp
hoelzl@31811
  2163
  have "case ?vs ! j of None \<Rightarrow> True | Some (l, u) \<Rightarrow> xs ! j \<in> { real l .. real u }"
hoelzl@31811
  2164
  proof (cases "?vs ! j")
hoelzl@31811
  2165
    case (Some b)
hoelzl@31811
  2166
    thus ?thesis
hoelzl@31811
  2167
    proof (cases "i = j")
hoelzl@31811
  2168
      case True
hoelzl@31811
  2169
      thus ?thesis using `?vs ! j = Some b` and bnd by auto
hoelzl@31811
  2170
    next
hoelzl@31811
  2171
      case False
hoelzl@31811
  2172
      thus ?thesis using `bounded_by xs vs` unfolding bounded_by_def by auto
hoelzl@31811
  2173
    qed
hoelzl@31811
  2174
  qed auto }
hoelzl@31811
  2175
  thus ?thesis unfolding bounded_by_def by auto
hoelzl@31811
  2176
qed
hoelzl@31811
  2177
hoelzl@31811
  2178
lemma bounded_by_None:
hoelzl@31811
  2179
  shows "bounded_by xs (replicate (length xs) None)"
hoelzl@31811
  2180
  unfolding bounded_by_def by auto
hoelzl@31811
  2181
hoelzl@31811
  2182
fun approx approx' :: "nat \<Rightarrow> floatarith \<Rightarrow> (float * float) option list \<Rightarrow> (float * float) option" where
hoelzl@29805
  2183
"approx' prec a bs          = (case (approx prec a bs) of Some (l, u) \<Rightarrow> Some (round_down prec l, round_up prec u) | None \<Rightarrow> None)" |
hoelzl@31811
  2184
"approx prec (Add a b) bs   = lift_bin' (approx' prec a bs) (approx' prec b bs) (\<lambda> l1 u1 l2 u2. (l1 + l2, u1 + u2))" |
hoelzl@29805
  2185
"approx prec (Minus a) bs   = lift_un' (approx' prec a bs) (\<lambda> l u. (-u, -l))" |
hoelzl@29805
  2186
"approx prec (Mult a b) bs  = lift_bin' (approx' prec a bs) (approx' prec b bs)
hoelzl@31809
  2187
                                    (\<lambda> a1 a2 b1 b2. (float_nprt a1 * float_pprt b2 + float_nprt a2 * float_nprt b2 + float_pprt a1 * float_pprt b1 + float_pprt a2 * float_nprt b1,
hoelzl@29805
  2188
                                                     float_pprt a2 * float_pprt b2 + float_pprt a1 * float_nprt b2 + float_nprt a2 * float_pprt b1 + float_nprt a1 * float_nprt b1))" |
hoelzl@29805
  2189
"approx prec (Inverse a) bs = lift_un (approx' prec a bs) (\<lambda> l u. if (0 < l \<or> u < 0) then (Some (float_divl prec 1 u), Some (float_divr prec 1 l)) else (None, None))" |
hoelzl@29805
  2190
"approx prec (Cos a) bs     = lift_un' (approx' prec a bs) (bnds_cos prec)" |
hoelzl@29805
  2191
"approx prec Pi bs          = Some (lb_pi prec, ub_pi prec)" |
hoelzl@29805
  2192
"approx prec (Min a b) bs   = lift_bin' (approx' prec a bs) (approx' prec b bs) (\<lambda> l1 u1 l2 u2. (min l1 l2, min u1 u2))" |
hoelzl@29805
  2193
"approx prec (Max a b) bs   = lift_bin' (approx' prec a bs) (approx' prec b bs) (\<lambda> l1 u1 l2 u2. (max l1 l2, max u1 u2))" |
hoelzl@29805
  2194
"approx prec (Abs a) bs     = lift_un' (approx' prec a bs) (\<lambda>l u. (if l < 0 \<and> 0 < u then 0 else min \<bar>l\<bar> \<bar>u\<bar>, max \<bar>l\<bar> \<bar>u\<bar>))" |
hoelzl@29805
  2195
"approx prec (Arctan a) bs  = lift_un' (approx' prec a bs) (\<lambda> l u. (lb_arctan prec l, ub_arctan prec u))" |
hoelzl@31467
  2196
"approx prec (Sqrt a) bs    = lift_un' (approx' prec a bs) (\<lambda> l u. (lb_sqrt prec l, ub_sqrt prec u))" |
hoelzl@29805
  2197
"approx prec (Exp a) bs     = lift_un' (approx' prec a bs) (\<lambda> l u. (lb_exp prec l, ub_exp prec u))" |
hoelzl@29805
  2198
"approx prec (Ln a) bs      = lift_un (approx' prec a bs) (\<lambda> l u. (lb_ln prec l, ub_ln prec u))" |
hoelzl@29805
  2199
"approx prec (Power a n) bs = lift_un' (approx' prec a bs) (float_power_bnds n)" |
hoelzl@29805
  2200
"approx prec (Num f) bs     = Some (f, f)" |
hoelzl@32919
  2201
"approx prec (Var i) bs    = (if i < length bs then bs ! i else None)"
hoelzl@29805
  2202
hoelzl@29805
  2203
lemma lift_bin'_ex:
hoelzl@29805
  2204
  assumes lift_bin'_Some: "Some (l, u) = lift_bin' a b f"
hoelzl@29805
  2205
  shows "\<exists> l1 u1 l2 u2. Some (l1, u1) = a \<and> Some (l2, u2) = b"
hoelzl@29805
  2206
proof (cases a)
hoelzl@29805
  2207
  case None hence "None = lift_bin' a b f" unfolding None lift_bin'.simps ..
hoelzl@29805
  2208
  thus ?thesis using lift_bin'_Some by auto
hoelzl@29805
  2209
next
hoelzl@29805
  2210
  case (Some a')
hoelzl@29805
  2211
  show ?thesis
hoelzl@29805
  2212
  proof (cases b)
hoelzl@29805
  2213
    case None hence "None = lift_bin' a b f" unfolding None lift_bin'.simps ..
hoelzl@29805
  2214
    thus ?thesis using lift_bin'_Some by auto
hoelzl@29805
  2215
  next
hoelzl@29805
  2216
    case (Some b')
hoelzl@29805
  2217
    obtain la ua where a': "a' = (la, ua)" by (cases a', auto)
hoelzl@29805
  2218
    obtain lb ub where b': "b' = (lb, ub)" by (cases b', auto)
hoelzl@29805
  2219
    thus ?thesis unfolding `a = Some a'` `b = Some b'` a' b' by auto
hoelzl@29805
  2220
  qed
hoelzl@29805
  2221
qed
hoelzl@29805
  2222
hoelzl@29805
  2223
lemma lift_bin'_f:
hoelzl@29805
  2224
  assumes lift_bin'_Some: "Some (l, u) = lift_bin' (g a) (g b) f"
hoelzl@29805
  2225
  and Pa: "\<And>l u. Some (l, u) = g a \<Longrightarrow> P l u a" and Pb: "\<And>l u. Some (l, u) = g b \<Longrightarrow> P l u b"
hoelzl@29805
  2226
  shows "\<exists> l1 u1 l2 u2. P l1 u1 a \<and> P l2 u2 b \<and> l = fst (f l1 u1 l2 u2) \<and> u = snd (f l1 u1 l2 u2)"
hoelzl@29805
  2227
proof -
hoelzl@29805
  2228
  obtain l1 u1 l2 u2
hoelzl@29805
  2229
    where Sa: "Some (l1, u1) = g a" and Sb: "Some (l2, u2) = g b" using lift_bin'_ex[OF assms(1)] by auto
hoelzl@31809
  2230
  have lu: "(l, u) = f l1 u1 l2 u2" using lift_bin'_Some[unfolded Sa[symmetric] Sb[symmetric] lift_bin'.simps] by auto
hoelzl@29805
  2231
  have "l = fst (f l1 u1 l2 u2)" and "u = snd (f l1 u1 l2 u2)" unfolding lu[symmetric] by auto
hoelzl@31809
  2232
  thus ?thesis using Pa[OF Sa] Pb[OF Sb] by auto
hoelzl@29805
  2233
qed
hoelzl@29805
  2234
hoelzl@29805
  2235
lemma approx_approx':
hoelzl@40881
  2236
  assumes Pa: "\<And>l u. Some (l, u) = approx prec a vs \<Longrightarrow> l \<le> interpret_floatarith a xs \<and> interpret_floatarith a xs \<le> u"
hoelzl@29805
  2237
  and approx': "Some (l, u) = approx' prec a vs"
hoelzl@40881
  2238
  shows "l \<le> interpret_floatarith a xs \<and> interpret_floatarith a xs \<le> u"
hoelzl@29805
  2239
proof -
hoelzl@29805
  2240
  obtain l' u' where S: "Some (l', u') = approx prec a vs"
hoelzl@29805
  2241
    using approx' unfolding approx'.simps by (cases "approx prec a vs", auto)
hoelzl@29805
  2242
  have l': "l = round_down prec l'" and u': "u = round_up prec u'"
hoelzl@29805
  2243
    using approx' unfolding approx'.simps S[symmetric] by auto
hoelzl@31809
  2244
  show ?thesis unfolding l' u'
hoelzl@29805
  2245
    using order_trans[OF Pa[OF S, THEN conjunct2] round_up[of u']]
hoelzl@29805
  2246
    using order_trans[OF round_down[of _ l'] Pa[OF S, THEN conjunct1]] by auto
hoelzl@29805
  2247
qed
hoelzl@29805
  2248
hoelzl@29805
  2249
lemma lift_bin':
hoelzl@29805
  2250
  assumes lift_bin'_Some: "Some (l, u) = lift_bin' (approx' prec a bs) (approx' prec b bs) f"
hoelzl@40881
  2251
  and Pa: "\<And>l u. Some (l, u) = approx prec a bs \<Longrightarrow> l \<le> interpret_floatarith a xs \<and> interpret_floatarith a xs \<le> u" (is "\<And>l u. _ = ?g a \<Longrightarrow> ?P l u a")
hoelzl@40881
  2252
  and Pb: "\<And>l u. Some (l, u) = approx prec b bs \<Longrightarrow> l \<le> interpret_floatarith b xs \<and> interpret_floatarith b xs \<le> u"
hoelzl@40881
  2253
  shows "\<exists> l1 u1 l2 u2. (l1 \<le> interpret_floatarith a xs \<and> interpret_floatarith a xs \<le> u1) \<and>
hoelzl@40881
  2254
                        (l2 \<le> interpret_floatarith b xs \<and> interpret_floatarith b xs \<le> u2) \<and>
hoelzl@29805
  2255
                        l = fst (f l1 u1 l2 u2) \<and> u = snd (f l1 u1 l2 u2)"
hoelzl@29805
  2256
proof -
hoelzl@29805
  2257
  { fix l u assume "Some (l, u) = approx' prec a bs"
hoelzl@29805
  2258
    with approx_approx'[of prec a bs, OF _ this] Pa
hoelzl@40881
  2259
    have "l \<le> interpret_floatarith a xs \<and> interpret_floatarith a xs \<le> u" by auto } note Pa = this
hoelzl@29805
  2260
  { fix l u assume "Some (l, u) = approx' prec b bs"
hoelzl@29805
  2261
    with approx_approx'[of prec b bs, OF _ this] Pb
hoelzl@40881
  2262
    have "l \<le> interpret_floatarith b xs \<and> interpret_floatarith b xs \<le> u" by auto } note Pb = this
hoelzl@29805
  2263
hoelzl@29805
  2264
  from lift_bin'_f[where g="\<lambda>a. approx' prec a bs" and P = ?P, OF lift_bin'_Some, OF Pa Pb]
hoelzl@29805
  2265
  show ?thesis by auto
hoelzl@29805
  2266
qed
hoelzl@29805
  2267
hoelzl@29805
  2268
lemma lift_un'_ex:
hoelzl@29805
  2269
  assumes lift_un'_Some: "Some (l, u) = lift_un' a f"
hoelzl@29805
  2270
  shows "\<exists> l u. Some (l, u) = a"
hoelzl@29805
  2271
proof (cases a)
hoelzl@29805
  2272
  case None hence "None = lift_un' a f" unfolding None lift_un'.simps ..
hoelzl@29805
  2273
  thus ?thesis using lift_un'_Some by auto
hoelzl@29805
  2274
next
hoelzl@29805
  2275
  case (Some a')
hoelzl@29805
  2276
  obtain la ua where a': "a' = (la, ua)" by (cases a', auto)
hoelzl@29805
  2277
  thus ?thesis unfolding `a = Some a'` a' by auto
hoelzl@29805
  2278
qed
hoelzl@29805
  2279
hoelzl@29805
  2280
lemma lift_un'_f:
hoelzl@29805
  2281
  assumes lift_un'_Some: "Some (l, u) = lift_un' (g a) f"
hoelzl@29805
  2282
  and Pa: "\<And>l u. Some (l, u) = g a \<Longrightarrow> P l u a"
hoelzl@29805
  2283
  shows "\<exists> l1 u1. P l1 u1 a \<and> l = fst (f l1 u1) \<and> u = snd (f l1 u1)"
hoelzl@29805
  2284
proof -
hoelzl@29805
  2285
  obtain l1 u1 where Sa: "Some (l1, u1) = g a" using lift_un'_ex[OF assms(1)] by auto