src/HOL/Complex.thy
author huffman
Thu Sep 08 07:06:59 2011 -0700 (2011-09-08)
changeset 44841 e55503200061
parent 44828 3d6a79e0e1d0
child 44842 282eef2c0f77
permissions -rw-r--r--
tuned
     1 (*  Title:       HOL/Complex.thy
     2     Author:      Jacques D. Fleuriot
     3     Copyright:   2001 University of Edinburgh
     4     Conversion to Isar and new proofs by Lawrence C Paulson, 2003/4
     5 *)
     6 
     7 header {* Complex Numbers: Rectangular and Polar Representations *}
     8 
     9 theory Complex
    10 imports Transcendental
    11 begin
    12 
    13 datatype complex = Complex real real
    14 
    15 primrec Re :: "complex \<Rightarrow> real"
    16   where Re: "Re (Complex x y) = x"
    17 
    18 primrec Im :: "complex \<Rightarrow> real"
    19   where Im: "Im (Complex x y) = y"
    20 
    21 lemma complex_surj [simp]: "Complex (Re z) (Im z) = z"
    22   by (induct z) simp
    23 
    24 lemma complex_eqI [intro?]: "\<lbrakk>Re x = Re y; Im x = Im y\<rbrakk> \<Longrightarrow> x = y"
    25   by (induct x, induct y) simp
    26 
    27 lemma complex_eq_iff: "x = y \<longleftrightarrow> Re x = Re y \<and> Im x = Im y"
    28   by (induct x, induct y) simp
    29 
    30 
    31 subsection {* Addition and Subtraction *}
    32 
    33 instantiation complex :: ab_group_add
    34 begin
    35 
    36 definition complex_zero_def:
    37   "0 = Complex 0 0"
    38 
    39 definition complex_add_def:
    40   "x + y = Complex (Re x + Re y) (Im x + Im y)"
    41 
    42 definition complex_minus_def:
    43   "- x = Complex (- Re x) (- Im x)"
    44 
    45 definition complex_diff_def:
    46   "x - (y\<Colon>complex) = x + - y"
    47 
    48 lemma Complex_eq_0 [simp]: "Complex a b = 0 \<longleftrightarrow> a = 0 \<and> b = 0"
    49   by (simp add: complex_zero_def)
    50 
    51 lemma complex_Re_zero [simp]: "Re 0 = 0"
    52   by (simp add: complex_zero_def)
    53 
    54 lemma complex_Im_zero [simp]: "Im 0 = 0"
    55   by (simp add: complex_zero_def)
    56 
    57 lemma complex_add [simp]:
    58   "Complex a b + Complex c d = Complex (a + c) (b + d)"
    59   by (simp add: complex_add_def)
    60 
    61 lemma complex_Re_add [simp]: "Re (x + y) = Re x + Re y"
    62   by (simp add: complex_add_def)
    63 
    64 lemma complex_Im_add [simp]: "Im (x + y) = Im x + Im y"
    65   by (simp add: complex_add_def)
    66 
    67 lemma complex_minus [simp]:
    68   "- (Complex a b) = Complex (- a) (- b)"
    69   by (simp add: complex_minus_def)
    70 
    71 lemma complex_Re_minus [simp]: "Re (- x) = - Re x"
    72   by (simp add: complex_minus_def)
    73 
    74 lemma complex_Im_minus [simp]: "Im (- x) = - Im x"
    75   by (simp add: complex_minus_def)
    76 
    77 lemma complex_diff [simp]:
    78   "Complex a b - Complex c d = Complex (a - c) (b - d)"
    79   by (simp add: complex_diff_def)
    80 
    81 lemma complex_Re_diff [simp]: "Re (x - y) = Re x - Re y"
    82   by (simp add: complex_diff_def)
    83 
    84 lemma complex_Im_diff [simp]: "Im (x - y) = Im x - Im y"
    85   by (simp add: complex_diff_def)
    86 
    87 instance
    88   by intro_classes (simp_all add: complex_add_def complex_diff_def)
    89 
    90 end
    91 
    92 
    93 subsection {* Multiplication and Division *}
    94 
    95 instantiation complex :: field_inverse_zero
    96 begin
    97 
    98 definition complex_one_def:
    99   "1 = Complex 1 0"
   100 
   101 definition complex_mult_def:
   102   "x * y = Complex (Re x * Re y - Im x * Im y) (Re x * Im y + Im x * Re y)"
   103 
   104 definition complex_inverse_def:
   105   "inverse x =
   106     Complex (Re x / ((Re x)\<twosuperior> + (Im x)\<twosuperior>)) (- Im x / ((Re x)\<twosuperior> + (Im x)\<twosuperior>))"
   107 
   108 definition complex_divide_def:
   109   "x / (y\<Colon>complex) = x * inverse y"
   110 
   111 lemma Complex_eq_1 [simp]: "(Complex a b = 1) = (a = 1 \<and> b = 0)"
   112   by (simp add: complex_one_def)
   113 
   114 lemma complex_Re_one [simp]: "Re 1 = 1"
   115   by (simp add: complex_one_def)
   116 
   117 lemma complex_Im_one [simp]: "Im 1 = 0"
   118   by (simp add: complex_one_def)
   119 
   120 lemma complex_mult [simp]:
   121   "Complex a b * Complex c d = Complex (a * c - b * d) (a * d + b * c)"
   122   by (simp add: complex_mult_def)
   123 
   124 lemma complex_Re_mult [simp]: "Re (x * y) = Re x * Re y - Im x * Im y"
   125   by (simp add: complex_mult_def)
   126 
   127 lemma complex_Im_mult [simp]: "Im (x * y) = Re x * Im y + Im x * Re y"
   128   by (simp add: complex_mult_def)
   129 
   130 lemma complex_inverse [simp]:
   131   "inverse (Complex a b) = Complex (a / (a\<twosuperior> + b\<twosuperior>)) (- b / (a\<twosuperior> + b\<twosuperior>))"
   132   by (simp add: complex_inverse_def)
   133 
   134 lemma complex_Re_inverse:
   135   "Re (inverse x) = Re x / ((Re x)\<twosuperior> + (Im x)\<twosuperior>)"
   136   by (simp add: complex_inverse_def)
   137 
   138 lemma complex_Im_inverse:
   139   "Im (inverse x) = - Im x / ((Re x)\<twosuperior> + (Im x)\<twosuperior>)"
   140   by (simp add: complex_inverse_def)
   141 
   142 instance
   143   by intro_classes (simp_all add: complex_mult_def
   144     right_distrib left_distrib right_diff_distrib left_diff_distrib
   145     complex_inverse_def complex_divide_def
   146     power2_eq_square add_divide_distrib [symmetric]
   147     complex_eq_iff)
   148 
   149 end
   150 
   151 
   152 subsection {* Numerals and Arithmetic *}
   153 
   154 instantiation complex :: number_ring
   155 begin
   156 
   157 definition complex_number_of_def:
   158   "number_of w = (of_int w \<Colon> complex)"
   159 
   160 instance
   161   by intro_classes (simp only: complex_number_of_def)
   162 
   163 end
   164 
   165 lemma complex_Re_of_nat [simp]: "Re (of_nat n) = of_nat n"
   166   by (induct n) simp_all
   167 
   168 lemma complex_Im_of_nat [simp]: "Im (of_nat n) = 0"
   169   by (induct n) simp_all
   170 
   171 lemma complex_Re_of_int [simp]: "Re (of_int z) = of_int z"
   172   by (cases z rule: int_diff_cases) simp
   173 
   174 lemma complex_Im_of_int [simp]: "Im (of_int z) = 0"
   175   by (cases z rule: int_diff_cases) simp
   176 
   177 lemma complex_Re_number_of [simp]: "Re (number_of v) = number_of v"
   178   unfolding number_of_eq by (rule complex_Re_of_int)
   179 
   180 lemma complex_Im_number_of [simp]: "Im (number_of v) = 0"
   181   unfolding number_of_eq by (rule complex_Im_of_int)
   182 
   183 lemma Complex_eq_number_of [simp]:
   184   "(Complex a b = number_of w) = (a = number_of w \<and> b = 0)"
   185   by (simp add: complex_eq_iff)
   186 
   187 
   188 subsection {* Scalar Multiplication *}
   189 
   190 instantiation complex :: real_field
   191 begin
   192 
   193 definition complex_scaleR_def:
   194   "scaleR r x = Complex (r * Re x) (r * Im x)"
   195 
   196 lemma complex_scaleR [simp]:
   197   "scaleR r (Complex a b) = Complex (r * a) (r * b)"
   198   unfolding complex_scaleR_def by simp
   199 
   200 lemma complex_Re_scaleR [simp]: "Re (scaleR r x) = r * Re x"
   201   unfolding complex_scaleR_def by simp
   202 
   203 lemma complex_Im_scaleR [simp]: "Im (scaleR r x) = r * Im x"
   204   unfolding complex_scaleR_def by simp
   205 
   206 instance
   207 proof
   208   fix a b :: real and x y :: complex
   209   show "scaleR a (x + y) = scaleR a x + scaleR a y"
   210     by (simp add: complex_eq_iff right_distrib)
   211   show "scaleR (a + b) x = scaleR a x + scaleR b x"
   212     by (simp add: complex_eq_iff left_distrib)
   213   show "scaleR a (scaleR b x) = scaleR (a * b) x"
   214     by (simp add: complex_eq_iff mult_assoc)
   215   show "scaleR 1 x = x"
   216     by (simp add: complex_eq_iff)
   217   show "scaleR a x * y = scaleR a (x * y)"
   218     by (simp add: complex_eq_iff algebra_simps)
   219   show "x * scaleR a y = scaleR a (x * y)"
   220     by (simp add: complex_eq_iff algebra_simps)
   221 qed
   222 
   223 end
   224 
   225 
   226 subsection{* Properties of Embedding from Reals *}
   227 
   228 abbreviation complex_of_real :: "real \<Rightarrow> complex"
   229   where "complex_of_real \<equiv> of_real"
   230 
   231 lemma complex_of_real_def: "complex_of_real r = Complex r 0"
   232   by (simp add: of_real_def complex_scaleR_def)
   233 
   234 lemma Re_complex_of_real [simp]: "Re (complex_of_real z) = z"
   235   by (simp add: complex_of_real_def)
   236 
   237 lemma Im_complex_of_real [simp]: "Im (complex_of_real z) = 0"
   238   by (simp add: complex_of_real_def)
   239 
   240 lemma Complex_add_complex_of_real [simp]:
   241   shows "Complex x y + complex_of_real r = Complex (x+r) y"
   242   by (simp add: complex_of_real_def)
   243 
   244 lemma complex_of_real_add_Complex [simp]:
   245   shows "complex_of_real r + Complex x y = Complex (r+x) y"
   246   by (simp add: complex_of_real_def)
   247 
   248 lemma Complex_mult_complex_of_real:
   249   shows "Complex x y * complex_of_real r = Complex (x*r) (y*r)"
   250   by (simp add: complex_of_real_def)
   251 
   252 lemma complex_of_real_mult_Complex:
   253   shows "complex_of_real r * Complex x y = Complex (r*x) (r*y)"
   254   by (simp add: complex_of_real_def)
   255 
   256 lemma complex_eq_cancel_iff2 [simp]:
   257   shows "(Complex x y = complex_of_real xa) = (x = xa & y = 0)"
   258   by (simp add: complex_of_real_def)
   259 
   260 lemma complex_split_polar:
   261      "\<exists>r a. z = complex_of_real r * (Complex (cos a) (sin a))"
   262   by (simp add: complex_eq_iff polar_Ex)
   263 
   264 
   265 subsection {* Vector Norm *}
   266 
   267 instantiation complex :: real_normed_field
   268 begin
   269 
   270 definition complex_norm_def:
   271   "norm z = sqrt ((Re z)\<twosuperior> + (Im z)\<twosuperior>)"
   272 
   273 abbreviation cmod :: "complex \<Rightarrow> real"
   274   where "cmod \<equiv> norm"
   275 
   276 definition complex_sgn_def:
   277   "sgn x = x /\<^sub>R cmod x"
   278 
   279 definition dist_complex_def:
   280   "dist x y = cmod (x - y)"
   281 
   282 definition open_complex_def:
   283   "open (S :: complex set) \<longleftrightarrow> (\<forall>x\<in>S. \<exists>e>0. \<forall>y. dist y x < e \<longrightarrow> y \<in> S)"
   284 
   285 lemmas cmod_def = complex_norm_def
   286 
   287 lemma complex_norm [simp]: "cmod (Complex x y) = sqrt (x\<twosuperior> + y\<twosuperior>)"
   288   by (simp add: complex_norm_def)
   289 
   290 instance proof
   291   fix r :: real and x y :: complex and S :: "complex set"
   292   show "0 \<le> norm x"
   293     by (induct x) simp
   294   show "(norm x = 0) = (x = 0)"
   295     by (induct x) simp
   296   show "norm (x + y) \<le> norm x + norm y"
   297     by (induct x, induct y)
   298        (simp add: real_sqrt_sum_squares_triangle_ineq)
   299   show "norm (scaleR r x) = \<bar>r\<bar> * norm x"
   300     by (induct x)
   301        (simp add: power_mult_distrib right_distrib [symmetric] real_sqrt_mult)
   302   show "norm (x * y) = norm x * norm y"
   303     by (induct x, induct y)
   304        (simp add: real_sqrt_mult [symmetric] power2_eq_square algebra_simps)
   305   show "sgn x = x /\<^sub>R cmod x"
   306     by (rule complex_sgn_def)
   307   show "dist x y = cmod (x - y)"
   308     by (rule dist_complex_def)
   309   show "open S \<longleftrightarrow> (\<forall>x\<in>S. \<exists>e>0. \<forall>y. dist y x < e \<longrightarrow> y \<in> S)"
   310     by (rule open_complex_def)
   311 qed
   312 
   313 end
   314 
   315 lemma cmod_unit_one: "cmod (Complex (cos a) (sin a)) = 1"
   316   by simp
   317 
   318 lemma cmod_complex_polar:
   319   "cmod (complex_of_real r * Complex (cos a) (sin a)) = abs r"
   320   by (simp add: norm_mult)
   321 
   322 lemma complex_Re_le_cmod: "Re x \<le> cmod x"
   323   unfolding complex_norm_def
   324   by (rule real_sqrt_sum_squares_ge1)
   325 
   326 lemma complex_mod_minus_le_complex_mod: "- cmod x \<le> cmod x"
   327   by (rule order_trans [OF _ norm_ge_zero], simp)
   328 
   329 lemma complex_mod_triangle_ineq2: "cmod(b + a) - cmod b \<le> cmod a"
   330   by (rule ord_le_eq_trans [OF norm_triangle_ineq2], simp)
   331 
   332 lemma abs_Re_le_cmod: "\<bar>Re x\<bar> \<le> cmod x"
   333   by (cases x) simp
   334 
   335 lemma abs_Im_le_cmod: "\<bar>Im x\<bar> \<le> cmod x"
   336   by (cases x) simp
   337 
   338 
   339 subsection {* Completeness of the Complexes *}
   340 
   341 lemma bounded_linear_Re: "bounded_linear Re"
   342   by (rule bounded_linear_intro [where K=1], simp_all add: complex_norm_def)
   343 
   344 lemma bounded_linear_Im: "bounded_linear Im"
   345   by (rule bounded_linear_intro [where K=1], simp_all add: complex_norm_def)
   346 
   347 lemmas tendsto_Re [tendsto_intros] =
   348   bounded_linear.tendsto [OF bounded_linear_Re]
   349 
   350 lemmas tendsto_Im [tendsto_intros] =
   351   bounded_linear.tendsto [OF bounded_linear_Im]
   352 
   353 lemmas isCont_Re [simp] = bounded_linear.isCont [OF bounded_linear_Re]
   354 lemmas isCont_Im [simp] = bounded_linear.isCont [OF bounded_linear_Im]
   355 lemmas Cauchy_Re = bounded_linear.Cauchy [OF bounded_linear_Re]
   356 lemmas Cauchy_Im = bounded_linear.Cauchy [OF bounded_linear_Im]
   357 
   358 lemma tendsto_Complex [tendsto_intros]:
   359   assumes "(f ---> a) F" and "(g ---> b) F"
   360   shows "((\<lambda>x. Complex (f x) (g x)) ---> Complex a b) F"
   361 proof (rule tendstoI)
   362   fix r :: real assume "0 < r"
   363   hence "0 < r / sqrt 2" by (simp add: divide_pos_pos)
   364   have "eventually (\<lambda>x. dist (f x) a < r / sqrt 2) F"
   365     using `(f ---> a) F` and `0 < r / sqrt 2` by (rule tendstoD)
   366   moreover
   367   have "eventually (\<lambda>x. dist (g x) b < r / sqrt 2) F"
   368     using `(g ---> b) F` and `0 < r / sqrt 2` by (rule tendstoD)
   369   ultimately
   370   show "eventually (\<lambda>x. dist (Complex (f x) (g x)) (Complex a b) < r) F"
   371     by (rule eventually_elim2)
   372        (simp add: dist_norm real_sqrt_sum_squares_less)
   373 qed
   374 
   375 instance complex :: banach
   376 proof
   377   fix X :: "nat \<Rightarrow> complex"
   378   assume X: "Cauchy X"
   379   from Cauchy_Re [OF X] have 1: "(\<lambda>n. Re (X n)) ----> lim (\<lambda>n. Re (X n))"
   380     by (simp add: Cauchy_convergent_iff convergent_LIMSEQ_iff)
   381   from Cauchy_Im [OF X] have 2: "(\<lambda>n. Im (X n)) ----> lim (\<lambda>n. Im (X n))"
   382     by (simp add: Cauchy_convergent_iff convergent_LIMSEQ_iff)
   383   have "X ----> Complex (lim (\<lambda>n. Re (X n))) (lim (\<lambda>n. Im (X n)))"
   384     using tendsto_Complex [OF 1 2] by simp
   385   thus "convergent X"
   386     by (rule convergentI)
   387 qed
   388 
   389 
   390 subsection {* The Complex Number $i$ *}
   391 
   392 definition "ii" :: complex  ("\<i>")
   393   where i_def: "ii \<equiv> Complex 0 1"
   394 
   395 lemma complex_Re_i [simp]: "Re ii = 0"
   396   by (simp add: i_def)
   397 
   398 lemma complex_Im_i [simp]: "Im ii = 1"
   399   by (simp add: i_def)
   400 
   401 lemma Complex_eq_i [simp]: "(Complex x y = ii) = (x = 0 \<and> y = 1)"
   402   by (simp add: i_def)
   403 
   404 lemma complex_i_not_zero [simp]: "ii \<noteq> 0"
   405   by (simp add: complex_eq_iff)
   406 
   407 lemma complex_i_not_one [simp]: "ii \<noteq> 1"
   408   by (simp add: complex_eq_iff)
   409 
   410 lemma complex_i_not_number_of [simp]: "ii \<noteq> number_of w"
   411   by (simp add: complex_eq_iff)
   412 
   413 lemma i_mult_Complex [simp]: "ii * Complex a b = Complex (- b) a"
   414   by (simp add: complex_eq_iff)
   415 
   416 lemma Complex_mult_i [simp]: "Complex a b * ii = Complex (- b) a"
   417   by (simp add: complex_eq_iff)
   418 
   419 lemma i_complex_of_real [simp]: "ii * complex_of_real r = Complex 0 r"
   420   by (simp add: i_def complex_of_real_def)
   421 
   422 lemma complex_of_real_i [simp]: "complex_of_real r * ii = Complex 0 r"
   423   by (simp add: i_def complex_of_real_def)
   424 
   425 lemma i_squared [simp]: "ii * ii = -1"
   426   by (simp add: i_def)
   427 
   428 lemma power2_i [simp]: "ii\<twosuperior> = -1"
   429   by (simp add: power2_eq_square)
   430 
   431 lemma inverse_i [simp]: "inverse ii = - ii"
   432   by (rule inverse_unique, simp)
   433 
   434 lemma complex_i_mult_minus [simp]: "ii * (ii * x) = - x"
   435   by (simp add: mult_assoc [symmetric])
   436 
   437 
   438 subsection {* Complex Conjugation *}
   439 
   440 definition cnj :: "complex \<Rightarrow> complex" where
   441   "cnj z = Complex (Re z) (- Im z)"
   442 
   443 lemma complex_cnj [simp]: "cnj (Complex a b) = Complex a (- b)"
   444   by (simp add: cnj_def)
   445 
   446 lemma complex_Re_cnj [simp]: "Re (cnj x) = Re x"
   447   by (simp add: cnj_def)
   448 
   449 lemma complex_Im_cnj [simp]: "Im (cnj x) = - Im x"
   450   by (simp add: cnj_def)
   451 
   452 lemma complex_cnj_cancel_iff [simp]: "(cnj x = cnj y) = (x = y)"
   453   by (simp add: complex_eq_iff)
   454 
   455 lemma complex_cnj_cnj [simp]: "cnj (cnj z) = z"
   456   by (simp add: cnj_def)
   457 
   458 lemma complex_cnj_zero [simp]: "cnj 0 = 0"
   459   by (simp add: complex_eq_iff)
   460 
   461 lemma complex_cnj_zero_iff [iff]: "(cnj z = 0) = (z = 0)"
   462   by (simp add: complex_eq_iff)
   463 
   464 lemma complex_cnj_add: "cnj (x + y) = cnj x + cnj y"
   465   by (simp add: complex_eq_iff)
   466 
   467 lemma complex_cnj_diff: "cnj (x - y) = cnj x - cnj y"
   468   by (simp add: complex_eq_iff)
   469 
   470 lemma complex_cnj_minus: "cnj (- x) = - cnj x"
   471   by (simp add: complex_eq_iff)
   472 
   473 lemma complex_cnj_one [simp]: "cnj 1 = 1"
   474   by (simp add: complex_eq_iff)
   475 
   476 lemma complex_cnj_mult: "cnj (x * y) = cnj x * cnj y"
   477   by (simp add: complex_eq_iff)
   478 
   479 lemma complex_cnj_inverse: "cnj (inverse x) = inverse (cnj x)"
   480   by (simp add: complex_inverse_def)
   481 
   482 lemma complex_cnj_divide: "cnj (x / y) = cnj x / cnj y"
   483   by (simp add: complex_divide_def complex_cnj_mult complex_cnj_inverse)
   484 
   485 lemma complex_cnj_power: "cnj (x ^ n) = cnj x ^ n"
   486   by (induct n, simp_all add: complex_cnj_mult)
   487 
   488 lemma complex_cnj_of_nat [simp]: "cnj (of_nat n) = of_nat n"
   489   by (simp add: complex_eq_iff)
   490 
   491 lemma complex_cnj_of_int [simp]: "cnj (of_int z) = of_int z"
   492   by (simp add: complex_eq_iff)
   493 
   494 lemma complex_cnj_number_of [simp]: "cnj (number_of w) = number_of w"
   495   by (simp add: complex_eq_iff)
   496 
   497 lemma complex_cnj_scaleR: "cnj (scaleR r x) = scaleR r (cnj x)"
   498   by (simp add: complex_eq_iff)
   499 
   500 lemma complex_mod_cnj [simp]: "cmod (cnj z) = cmod z"
   501   by (simp add: complex_norm_def)
   502 
   503 lemma complex_cnj_complex_of_real [simp]: "cnj (of_real x) = of_real x"
   504   by (simp add: complex_eq_iff)
   505 
   506 lemma complex_cnj_i [simp]: "cnj ii = - ii"
   507   by (simp add: complex_eq_iff)
   508 
   509 lemma complex_add_cnj: "z + cnj z = complex_of_real (2 * Re z)"
   510   by (simp add: complex_eq_iff)
   511 
   512 lemma complex_diff_cnj: "z - cnj z = complex_of_real (2 * Im z) * ii"
   513   by (simp add: complex_eq_iff)
   514 
   515 lemma complex_mult_cnj: "z * cnj z = complex_of_real ((Re z)\<twosuperior> + (Im z)\<twosuperior>)"
   516   by (simp add: complex_eq_iff power2_eq_square)
   517 
   518 lemma complex_mod_mult_cnj: "cmod (z * cnj z) = (cmod z)\<twosuperior>"
   519   by (simp add: norm_mult power2_eq_square)
   520 
   521 lemma complex_mod_sqrt_Re_mult_cnj: "cmod z = sqrt (Re (z * cnj z))"
   522   by (simp add: cmod_def power2_eq_square)
   523 
   524 lemma complex_In_mult_cnj_zero [simp]: "Im (z * cnj z) = 0"
   525   by simp
   526 
   527 lemma bounded_linear_cnj: "bounded_linear cnj"
   528   using complex_cnj_add complex_cnj_scaleR
   529   by (rule bounded_linear_intro [where K=1], simp)
   530 
   531 lemmas tendsto_cnj [tendsto_intros] =
   532   bounded_linear.tendsto [OF bounded_linear_cnj]
   533 
   534 lemmas isCont_cnj [simp] =
   535   bounded_linear.isCont [OF bounded_linear_cnj]
   536 
   537 
   538 subsection {* Complex Signum and Argument *}
   539 
   540 definition arg :: "complex => real" where
   541   "arg z = (SOME a. Re(sgn z) = cos a & Im(sgn z) = sin a & -pi < a & a \<le> pi)"
   542 
   543 lemma sgn_eq: "sgn z = z / complex_of_real (cmod z)"
   544   by (simp add: sgn_div_norm divide_inverse scaleR_conv_of_real mult_commute)
   545 
   546 lemma Re_sgn [simp]: "Re(sgn z) = Re(z)/cmod z"
   547   by (simp add: complex_sgn_def divide_inverse)
   548 
   549 lemma Im_sgn [simp]: "Im(sgn z) = Im(z)/cmod z"
   550   by (simp add: complex_sgn_def divide_inverse)
   551 
   552 lemma complex_inverse_complex_split:
   553      "inverse(complex_of_real x + ii * complex_of_real y) =
   554       complex_of_real(x/(x ^ 2 + y ^ 2)) -
   555       ii * complex_of_real(y/(x ^ 2 + y ^ 2))"
   556   by (simp add: complex_of_real_def i_def diff_minus divide_inverse)
   557 
   558 (*----------------------------------------------------------------------------*)
   559 (* Many of the theorems below need to be moved elsewhere e.g. Transc. Also *)
   560 (* many of the theorems are not used - so should they be kept?                *)
   561 (*----------------------------------------------------------------------------*)
   562 
   563 lemma cos_arg_i_mult_zero_pos:
   564    "0 < y ==> cos (arg(Complex 0 y)) = 0"
   565 apply (simp add: arg_def abs_if)
   566 apply (rule_tac a = "pi/2" in someI2, auto)
   567 apply (rule order_less_trans [of _ 0], auto)
   568 done
   569 
   570 lemma cos_arg_i_mult_zero_neg:
   571    "y < 0 ==> cos (arg(Complex 0 y)) = 0"
   572 apply (simp add: arg_def abs_if)
   573 apply (rule_tac a = "- pi/2" in someI2, auto)
   574 apply (rule order_trans [of _ 0], auto)
   575 done
   576 
   577 lemma cos_arg_i_mult_zero [simp]:
   578      "y \<noteq> 0 ==> cos (arg(Complex 0 y)) = 0"
   579 by (auto simp add: linorder_neq_iff cos_arg_i_mult_zero_pos cos_arg_i_mult_zero_neg)
   580 
   581 
   582 subsection{*Finally! Polar Form for Complex Numbers*}
   583 
   584 subsubsection {* $\cos \theta + i \sin \theta$ *}
   585 
   586 definition cis :: "real \<Rightarrow> complex" where
   587   "cis a = Complex (cos a) (sin a)"
   588 
   589 lemma Re_cis [simp]: "Re (cis a) = cos a"
   590   by (simp add: cis_def)
   591 
   592 lemma Im_cis [simp]: "Im (cis a) = sin a"
   593   by (simp add: cis_def)
   594 
   595 lemma cis_zero [simp]: "cis 0 = 1"
   596   by (simp add: cis_def)
   597 
   598 lemma norm_cis [simp]: "norm (cis a) = 1"
   599   by (simp add: cis_def)
   600 
   601 lemma sgn_cis [simp]: "sgn (cis a) = cis a"
   602   by (simp add: sgn_div_norm)
   603 
   604 lemma cis_neq_zero [simp]: "cis a \<noteq> 0"
   605   by (metis norm_cis norm_zero zero_neq_one)
   606 
   607 lemma cis_mult: "cis a * cis b = cis (a + b)"
   608   by (simp add: cis_def cos_add sin_add)
   609 
   610 lemma DeMoivre: "(cis a) ^ n = cis (real n * a)"
   611   by (induct n, simp_all add: real_of_nat_Suc algebra_simps cis_mult)
   612 
   613 lemma cis_inverse [simp]: "inverse(cis a) = cis (-a)"
   614   by (simp add: cis_def)
   615 
   616 lemma cis_divide: "cis a / cis b = cis (a - b)"
   617   by (simp add: complex_divide_def cis_mult diff_minus)
   618 
   619 lemma cos_n_Re_cis_pow_n: "cos (real n * a) = Re(cis a ^ n)"
   620   by (auto simp add: DeMoivre)
   621 
   622 lemma sin_n_Im_cis_pow_n: "sin (real n * a) = Im(cis a ^ n)"
   623   by (auto simp add: DeMoivre)
   624 
   625 subsubsection {* $r(\cos \theta + i \sin \theta)$ *}
   626 
   627 definition rcis :: "[real, real] \<Rightarrow> complex" where
   628   "rcis r a = complex_of_real r * cis a"
   629 
   630 lemma Re_rcis [simp]: "Re(rcis r a) = r * cos a"
   631   by (simp add: rcis_def)
   632 
   633 lemma Im_rcis [simp]: "Im(rcis r a) = r * sin a"
   634   by (simp add: rcis_def)
   635 
   636 lemma rcis_Ex: "\<exists>r a. z = rcis r a"
   637   by (simp add: complex_eq_iff polar_Ex)
   638 
   639 lemma complex_mod_rcis [simp]: "cmod(rcis r a) = abs r"
   640   by (simp add: rcis_def norm_mult)
   641 
   642 lemma cis_rcis_eq: "cis a = rcis 1 a"
   643   by (simp add: rcis_def)
   644 
   645 lemma rcis_mult: "rcis r1 a * rcis r2 b = rcis (r1*r2) (a + b)"
   646   by (simp add: rcis_def cis_mult)
   647 
   648 lemma rcis_zero_mod [simp]: "rcis 0 a = 0"
   649   by (simp add: rcis_def)
   650 
   651 lemma rcis_zero_arg [simp]: "rcis r 0 = complex_of_real r"
   652   by (simp add: rcis_def)
   653 
   654 lemma rcis_eq_zero_iff [simp]: "rcis r a = 0 \<longleftrightarrow> r = 0"
   655   by (simp add: rcis_def)
   656 
   657 lemma DeMoivre2: "(rcis r a) ^ n = rcis (r ^ n) (real n * a)"
   658   by (simp add: rcis_def power_mult_distrib DeMoivre)
   659 
   660 lemma rcis_inverse: "inverse(rcis r a) = rcis (1/r) (-a)"
   661   by (simp add: divide_inverse rcis_def)
   662 
   663 lemma rcis_divide: "rcis r1 a / rcis r2 b = rcis (r1/r2) (a - b)"
   664   by (simp add: rcis_def cis_divide [symmetric])
   665 
   666 subsubsection {* Complex exponential *}
   667 
   668 abbreviation expi :: "complex \<Rightarrow> complex"
   669   where "expi \<equiv> exp"
   670 
   671 lemma cis_conv_exp: "cis b = exp (Complex 0 b)"
   672 proof (rule complex_eqI)
   673   { fix n have "Complex 0 b ^ n =
   674     real (fact n) *\<^sub>R Complex (cos_coeff n * b ^ n) (sin_coeff n * b ^ n)"
   675       apply (induct n)
   676       apply (simp add: cos_coeff_def sin_coeff_def)
   677       apply (simp add: sin_coeff_Suc cos_coeff_Suc del: mult_Suc)
   678       done } note * = this
   679   show "Re (cis b) = Re (exp (Complex 0 b))"
   680     unfolding exp_def cis_def cos_def
   681     by (subst bounded_linear.suminf[OF bounded_linear_Re summable_exp_generic],
   682       simp add: * mult_assoc [symmetric])
   683   show "Im (cis b) = Im (exp (Complex 0 b))"
   684     unfolding exp_def cis_def sin_def
   685     by (subst bounded_linear.suminf[OF bounded_linear_Im summable_exp_generic],
   686       simp add: * mult_assoc [symmetric])
   687 qed
   688 
   689 lemma expi_def: "expi z = complex_of_real (exp (Re z)) * cis (Im z)"
   690   unfolding cis_conv_exp exp_of_real [symmetric] mult_exp_exp by simp
   691 
   692 lemma Re_exp: "Re (exp z) = exp (Re z) * cos (Im z)"
   693   unfolding expi_def by simp
   694 
   695 lemma Im_exp: "Im (exp z) = exp (Re z) * sin (Im z)"
   696   unfolding expi_def by simp
   697 
   698 lemma complex_expi_Ex: "\<exists>a r. z = complex_of_real r * expi a"
   699 apply (insert rcis_Ex [of z])
   700 apply (auto simp add: expi_def rcis_def mult_assoc [symmetric])
   701 apply (rule_tac x = "ii * complex_of_real a" in exI, auto)
   702 done
   703 
   704 lemma expi_two_pi_i [simp]: "expi((2::complex) * complex_of_real pi * ii) = 1"
   705   by (simp add: expi_def cis_def)
   706 
   707 text {* Legacy theorem names *}
   708 
   709 lemmas expand_complex_eq = complex_eq_iff
   710 lemmas complex_Re_Im_cancel_iff = complex_eq_iff
   711 lemmas complex_equality = complex_eqI
   712 
   713 end