paulson@10751: (*  Title       : Series.thy
paulson@10751:     Author      : Jacques D. Fleuriot
paulson@10751:     Copyright   : 1998  University of Cambridge
paulson@14416: 
paulson@14416: Converted to Isar and polished by lcp
nipkow@15539: Converted to setsum and polished yet more by TNN
paulson@10751: *) 
paulson@10751: 
paulson@14416: header{*Finite Summation and Infinite Series*}
paulson@10751: 
nipkow@15131: theory Series
nipkow@15140: imports SEQ Lim
nipkow@15131: begin
paulson@10751: 
nipkow@15539: (* FIXME why not globally? *)
nipkow@15536: declare atLeastLessThan_empty[simp];
nipkow@15539: declare atLeastLessThan_iff[iff]
paulson@10751: 
paulson@10751: constdefs
paulson@14416:    sums  :: "[nat=>real,real] => bool"     (infixr "sums" 80)
nipkow@15536:    "f sums s  == (%n. setsum f {0..<n}) ----> s"
paulson@10751: 
paulson@14416:    summable :: "(nat=>real) => bool"
paulson@14416:    "summable f == (\<exists>s. f sums s)"
paulson@14416: 
paulson@14416:    suminf   :: "(nat=>real) => real"
nipkow@15539:    "suminf f == SOME s. f sums s"
paulson@14416: 
nipkow@15539: lemma setsum_Suc[simp]:
nipkow@15536:   "setsum f {m..<Suc n} = (if n < m then 0 else setsum f {m..<n} + f(n))"
nipkow@15536: by (simp add: atLeastLessThanSuc add_commute)
paulson@14416: 
nipkow@15536: (*
paulson@14416: lemma sumr_add: "sumr m n f + sumr m n g = sumr m n (%n. f n + g n)"
paulson@15047: by (simp add: setsum_addf)
paulson@14416: 
paulson@15047: lemma sumr_mult: "r * sumr m n (f::nat=>real) = sumr m n (%n. r * f n)"
paulson@15047: by (simp add: setsum_mult)
paulson@14416: 
paulson@14416: lemma sumr_split_add [rule_format]:
paulson@15047:      "n < p --> sumr 0 n f + sumr n p f = sumr 0 p (f::nat=>real)"
paulson@15251: apply (induct "p", auto)
paulson@14416: apply (rename_tac k) 
paulson@14416: apply (subgoal_tac "n=k", auto) 
paulson@14416: done
nipkow@15536: 
nipkow@15536: lemma sumr_split_add: "\<lbrakk> m \<le> n; n \<le> p \<rbrakk> \<Longrightarrow>
nipkow@15536:   setsum f {m..<n} + setsum f {n..<p} = setsum f {m..<p::nat}"
nipkow@15536: by (simp add:setsum_Un_disjoint[symmetric] ivl_disj_int ivl_disj_un)
paulson@14416: 
paulson@15047: lemma sumr_split_add_minus:
nipkow@15537: fixes f :: "nat \<Rightarrow> 'a::ab_group_add"
nipkow@15537: shows "\<lbrakk> m \<le> n; n \<le> p \<rbrakk> \<Longrightarrow>
nipkow@15537:   setsum f {m..<p} - setsum f {m..<n} = setsum f {n..<p}"
nipkow@15537: using sumr_split_add [of m n p f,symmetric]
paulson@14416: apply (simp add: add_ac)
paulson@14416: done
nipkow@15539: *)
paulson@14416: 
nipkow@15539: lemma sumr_diff_mult_const:
nipkow@15539:  "setsum f {0..<n} - (real n*r) = setsum (%i. f i - r) {0..<n::nat}"
nipkow@15536: by (simp add: diff_minus setsum_addf real_of_nat_def)
nipkow@15536: 
nipkow@15536: (*
paulson@15047: lemma sumr_rabs: "abs(sumr m n  (f::nat=>real)) \<le> sumr m n (%i. abs(f i))"
paulson@15047: by (simp add: setsum_abs)
paulson@14416: 
paulson@15047: lemma sumr_rabs_ge_zero [iff]: "0 \<le> sumr m n (%n. abs (f n))"
paulson@15047: by (simp add: setsum_abs_ge_zero)
paulson@14416: 
paulson@15047: text{*Just a congruence rule*}
paulson@15047: lemma sumr_fun_eq:
paulson@15047:      "(\<forall>r. m \<le> r & r < n --> f r = g r) ==> sumr m n f = sumr m n g"
paulson@15047: by (auto intro: setsum_cong) 
paulson@14416: 
paulson@15047: lemma sumr_less_bounds_zero [simp]: "n < m ==> sumr m n f = 0"
paulson@15047: by (simp add: atLeastLessThan_empty)
paulson@14416: 
paulson@14416: lemma sumr_minus: "sumr m n (%i. - f i) = - sumr m n f"
paulson@15047: by (simp add: Finite_Set.setsum_negf)
nipkow@15539: 
nipkow@15539: lemma sumr_shift_bounds:
nipkow@15539:   "setsum f {m+k..<n+k} = setsum (%i. f(i + k)){m..<n::nat}"
nipkow@15539: by (induct "n", auto)
nipkow@15536: *)
paulson@14416: 
nipkow@15539: (* Generalize from real to some algebraic structure? *)
nipkow@15539: lemma sumr_minus_one_realpow_zero [simp]:
nipkow@15539:   "setsum (%i. (-1) ^ Suc i) {0..<2*n} = (0::real)"
paulson@15251: by (induct "n", auto)
paulson@14416: 
nipkow@15539: (*
nipkow@15539: lemma sumr_interval_const2:
nipkow@15539:      "[|\<forall>n\<ge>m. f n = r; m \<le> k|]
nipkow@15539:       ==> sumr m k f = (real (k - m) * r)"
nipkow@15539: apply (induct "k", auto)
paulson@15251: apply (drule_tac x = k in spec)
paulson@14416: apply (auto dest!: le_imp_less_or_eq)
paulson@15047: apply (simp add: left_distrib real_of_nat_Suc split: nat_diff_split)
paulson@14416: done
nipkow@15539: *)
nipkow@15539: (* FIXME split in tow steps
nipkow@15539: lemma setsum_nat_set_real_const:
nipkow@15539:   "(\<And>n. n\<in>A \<Longrightarrow> f n = r) \<Longrightarrow> setsum f A = real(card A) * r" (is "PROP ?P")
nipkow@15539: proof (cases "finite A")
nipkow@15539:   case True
nipkow@15539:   thus "PROP ?P"
nipkow@15539:   proof induct
nipkow@15539:     case empty thus ?case by simp
nipkow@15539:   next
nipkow@15539:     case insert thus ?case by(simp add: left_distrib real_of_nat_Suc)
nipkow@15539:   qed
nipkow@15539: next
nipkow@15539:   case False thus "PROP ?P" by (simp add: setsum_def)
nipkow@15539: qed
nipkow@15539:  *)
paulson@14416: 
nipkow@15539: (*
nipkow@15539: lemma sumr_le:
nipkow@15539:      "[|\<forall>n\<ge>m. 0 \<le> (f n::real); m < k|] ==> setsum f {0..<m} \<le> setsum f {0..<k::nat}"
nipkow@15539: apply (induct "k")
nipkow@15539: apply (auto simp add: less_Suc_eq_le)
nipkow@15539: apply (drule_tac x = k in spec, safe)
nipkow@15539: apply (drule le_imp_less_or_eq, safe)
nipkow@15539: apply (arith)
nipkow@15539: apply (drule_tac a = "sumr 0 m f" in order_refl [THEN add_mono], auto)
paulson@14416: done
paulson@14416: 
paulson@15251: lemma sumr_le:
nipkow@15360:      "[|\<forall>n\<ge>m. 0 \<le> f n; m < k|] ==> sumr 0 m f \<le> sumr 0 k f"
paulson@15251: apply (induct "k")
paulson@14416: apply (auto simp add: less_Suc_eq_le)
paulson@15251: apply (drule_tac x = k in spec, safe)
paulson@14416: apply (drule le_imp_less_or_eq, safe)
paulson@15047: apply (arith) 
paulson@14416: apply (drule_tac a = "sumr 0 m f" in order_refl [THEN add_mono], auto)
paulson@14416: done
paulson@14416: 
paulson@14416: lemma sumr_le2 [rule_format (no_asm)]:
paulson@14416:      "(\<forall>r. m \<le> r & r < n --> f r \<le> g r) --> sumr m n f \<le> sumr m n g"
paulson@15251: apply (induct "n")
paulson@14416: apply (auto intro: add_mono simp add: le_def)
paulson@14416: done
nipkow@15539: *)
paulson@14416: 
nipkow@15539: (*
nipkow@15360: lemma sumr_ge_zero: "(\<forall>n\<ge>m. 0 \<le> f n) --> 0 \<le> sumr m n f"
paulson@15251: apply (induct "n", auto)
paulson@14416: apply (drule_tac x = n in spec, arith)
paulson@14416: done
nipkow@15539: *)
paulson@14416: 
nipkow@15539: (*
paulson@14416: lemma rabs_sumr_rabs_cancel [simp]:
paulson@15229:      "abs (sumr m n (%k. abs (f k))) = (sumr m n (%k. abs (f k)))"
paulson@15251: by (induct "n", simp_all add: add_increasing)
paulson@14416: 
paulson@14416: lemma sumr_zero [rule_format]:
nipkow@15360:      "\<forall>n \<ge> N. f n = 0 ==> N \<le> m --> sumr m n f = 0"
paulson@15251: by (induct "n", auto)
nipkow@15539: *)
paulson@14416: 
paulson@14416: lemma Suc_le_imp_diff_ge2:
nipkow@15539:      "[|\<forall>n \<ge> N. f (Suc n) = 0; Suc N \<le> m|] ==> setsum f {m..<n} = 0"
nipkow@15539: apply (rule setsum_0')
paulson@14416: apply (case_tac "n", auto)
nipkow@15539: apply(erule_tac x = "a - 1" in allE)
nipkow@15539: apply (simp split:nat_diff_split)
paulson@14416: done
paulson@14416: 
nipkow@15539: (* FIXME this is an awful lemma! *)
nipkow@15539: lemma sumr_one_lb_realpow_zero [simp]:
nipkow@15539:   "(\<Sum>n=Suc 0..<n. f(n) * (0::real) ^ n) = 0"
paulson@15251: apply (induct "n")
paulson@14416: apply (case_tac [2] "n", auto)
paulson@14416: done
nipkow@15536: (*
paulson@14416: lemma sumr_diff: "sumr m n f - sumr m n g = sumr m n (%n. f n - g n)"
nipkow@15536: by (simp add: diff_minus setsum_addf setsum_negf)
nipkow@15536: *)
nipkow@15539: (*
paulson@14416: lemma sumr_subst [rule_format (no_asm)]:
paulson@14416:      "(\<forall>p. m \<le> p & p < m+n --> (f p = g p)) --> sumr m n f = sumr m n g"
paulson@15251: by (induct "n", auto)
nipkow@15539: *)
paulson@14416: 
nipkow@15539: lemma setsum_bounded:
nipkow@15539:   assumes le: "\<And>i. i\<in>A \<Longrightarrow> f i \<le> (K::'a::{comm_semiring_1_cancel, pordered_ab_semigroup_add})"
nipkow@15539:   shows "setsum f A \<le> of_nat(card A) * K"
nipkow@15539: proof (cases "finite A")
nipkow@15539:   case True
nipkow@15539:   thus ?thesis using le setsum_mono[where K=A and g = "%x. K"] by simp
nipkow@15539: next
nipkow@15539:   case False thus ?thesis by (simp add: setsum_def)
nipkow@15539: qed
nipkow@15539: (*
paulson@14416: lemma sumr_bound [rule_format (no_asm)]:
paulson@14416:      "(\<forall>p. m \<le> p & p < m + n --> (f(p) \<le> K))  
nipkow@15539:       --> setsum f {m..<m+n::nat} \<le> (real n * K)"
paulson@15251: apply (induct "n")
paulson@14416: apply (auto intro: add_mono simp add: left_distrib real_of_nat_Suc)
paulson@14416: done
nipkow@15539: *)
nipkow@15539: (* FIXME should be generalized
paulson@14416: lemma sumr_bound2 [rule_format (no_asm)]:
paulson@14416:      "(\<forall>p. 0 \<le> p & p < n --> (f(p) \<le> K))  
nipkow@15539:       --> setsum f {0..<n::nat} \<le> (real n * K)"
paulson@15251: apply (induct "n")
paulson@15047: apply (auto intro: add_mono simp add: left_distrib real_of_nat_Suc add_commute)
paulson@14416: done
nipkow@15539:  *)
nipkow@15539: (* FIXME a bit specialized for [simp]! *)
paulson@14416: lemma sumr_group [simp]:
nipkow@15539:      "(\<Sum>m=0..<n::nat. setsum f {m * k ..< m*k + k}) = setsum f {0 ..< n * k}"
nipkow@15539: apply (subgoal_tac "k = 0 | 0 < k", auto simp:setsum_0')
paulson@15251: apply (induct "n")
nipkow@15539: apply (simp_all add: setsum_add_nat_ivl add_commute)
paulson@14416: done
nipkow@15539: (* FIXME setsum_0[simp] *)
nipkow@15539: 
paulson@14416: 
paulson@14416: subsection{* Infinite Sums, by the Properties of Limits*}
paulson@14416: 
paulson@14416: (*----------------------
paulson@14416:    suminf is the sum   
paulson@14416:  ---------------------*)
paulson@14416: lemma sums_summable: "f sums l ==> summable f"
paulson@14416: by (simp add: sums_def summable_def, blast)
paulson@14416: 
paulson@14416: lemma summable_sums: "summable f ==> f sums (suminf f)"
paulson@14416: apply (simp add: summable_def suminf_def)
paulson@14416: apply (blast intro: someI2)
paulson@14416: done
paulson@14416: 
paulson@14416: lemma summable_sumr_LIMSEQ_suminf: 
nipkow@15539:      "summable f ==> (%n. setsum f {0..<n}) ----> (suminf f)"
paulson@14416: apply (simp add: summable_def suminf_def sums_def)
paulson@14416: apply (blast intro: someI2)
paulson@14416: done
paulson@14416: 
paulson@14416: (*-------------------
paulson@14416:     sum is unique                    
paulson@14416:  ------------------*)
paulson@14416: lemma sums_unique: "f sums s ==> (s = suminf f)"
paulson@14416: apply (frule sums_summable [THEN summable_sums])
paulson@14416: apply (auto intro!: LIMSEQ_unique simp add: sums_def)
paulson@14416: done
paulson@14416: 
paulson@14416: (*
paulson@14416: Goalw [sums_def,LIMSEQ_def] 
paulson@14416:      "(\<forall>m. n \<le> Suc m --> f(m) = 0) ==> f sums (sumr 0 n f)"
paulson@14416: by safe
paulson@14416: by (res_inst_tac [("x","n")] exI 1);
paulson@14416: by (safe THEN ftac le_imp_less_or_eq 1)
paulson@14416: by safe
paulson@14416: by (dres_inst_tac [("f","f")] sumr_split_add_minus 1);
paulson@14416: by (ALLGOALS (Asm_simp_tac));
paulson@14416: by (dtac (conjI RS sumr_interval_const) 1);
paulson@14416: by Auto_tac
paulson@14416: qed "series_zero";
paulson@14416: next one was called series_zero2
paulson@14416: **********************)
paulson@14416: 
nipkow@15539: lemma ivl_subset[simp]:
nipkow@15539:  "({i..<j} \<subseteq> {m..<n}) = (j \<le> i | m \<le> i & j \<le> (n::'a::linorder))"
nipkow@15539: apply(auto simp:linorder_not_le)
nipkow@15539: apply(rule ccontr)
nipkow@15539: apply(frule subsetCE[where c = n])
nipkow@15539: apply(auto simp:linorder_not_le)
nipkow@15539: done
nipkow@15539: 
nipkow@15539: lemma ivl_diff[simp]:
nipkow@15539:  "i \<le> n \<Longrightarrow> {i..<m} - {i..<n} = {n..<(m::'a::linorder)}"
nipkow@15539: by(auto)
nipkow@15539: 
nipkow@15539: 
nipkow@15539: (* FIXME the last step should work w/o Ball_def, ideally just with
nipkow@15539:    setsum_0 and setsum_cong. Currently the simplifier does not simplify
nipkow@15539:    the premise x:{i..<j} that ball_cong (or a modified version of setsum_0')
nipkow@15539:    generates. FIX simplifier??? *)
paulson@14416: lemma series_zero: 
nipkow@15539:      "(\<forall>m. n \<le> m --> f(m) = 0) ==> f sums (setsum f {0..<n})"
nipkow@15537: apply (simp add: sums_def LIMSEQ_def diff_minus[symmetric], safe)
paulson@14416: apply (rule_tac x = n in exI)
nipkow@15539: apply (clarsimp simp add:setsum_diff[symmetric] setsum_0' Ball_def)
paulson@14416: done
paulson@14416: 
nipkow@15539: 
paulson@14416: lemma sums_mult: "x sums x0 ==> (%n. c * x(n)) sums (c * x0)"
nipkow@15536: by (auto simp add: sums_def setsum_mult [symmetric]
paulson@14416:          intro!: LIMSEQ_mult intro: LIMSEQ_const)
paulson@14416: 
paulson@14416: lemma sums_divide: "x sums x' ==> (%n. x(n)/c) sums (x'/c)"
paulson@14416: by (simp add: real_divide_def sums_mult mult_commute [of _ "inverse c"])
paulson@14416: 
paulson@14416: lemma sums_diff: "[| x sums x0; y sums y0 |] ==> (%n. x n - y n) sums (x0-y0)"
nipkow@15536: by (auto simp add: sums_def setsum_subtractf intro: LIMSEQ_diff)
paulson@14416: 
paulson@14416: lemma suminf_mult: "summable f ==> suminf f * c = suminf(%n. f n * c)"
paulson@14416: by (auto intro!: sums_unique sums_mult summable_sums simp add: mult_commute)
paulson@14416: 
paulson@14416: lemma suminf_mult2: "summable f ==> c * suminf f  = suminf(%n. c * f n)"
paulson@14416: by (auto intro!: sums_unique sums_mult summable_sums)
paulson@14416: 
paulson@14416: lemma suminf_diff:
paulson@14416:      "[| summable f; summable g |]   
paulson@14416:       ==> suminf f - suminf g  = suminf(%n. f n - g n)"
paulson@14416: by (auto intro!: sums_diff sums_unique summable_sums)
paulson@14416: 
paulson@14416: lemma sums_minus: "x sums x0 ==> (%n. - x n) sums - x0"
nipkow@15536: by (auto simp add: sums_def intro!: LIMSEQ_minus simp add: setsum_negf)
paulson@14416: 
paulson@14416: lemma sums_group:
nipkow@15539:      "[|summable f; 0 < k |] ==> (%n. setsum f {n*k..<n*k+k}) sums (suminf f)"
paulson@14416: apply (drule summable_sums)
paulson@14416: apply (auto simp add: sums_def LIMSEQ_def)
paulson@14416: apply (drule_tac x = r in spec, safe)
paulson@14416: apply (rule_tac x = no in exI, safe)
paulson@14416: apply (drule_tac x = "n*k" in spec)
paulson@14416: apply (auto dest!: not_leE)
paulson@14416: apply (drule_tac j = no in less_le_trans, auto)
paulson@14416: done
paulson@14416: 
paulson@14416: lemma sumr_pos_lt_pair_lemma:
nipkow@15539:   "[|\<forall>d. - f (n + (d + d)) < (f (Suc (n + (d + d))) :: real) |]
nipkow@15539:    ==> setsum f {0..<n+Suc(Suc 0)} \<le> setsum f {0..<Suc(Suc 0) * Suc no + n}"
paulson@15251: apply (induct "no", auto)
paulson@15251: apply (drule_tac x = "Suc no" in spec)
nipkow@15539: apply (simp add: add_ac)
paulson@14416: done
paulson@10751: 
paulson@10751: 
paulson@14416: lemma sumr_pos_lt_pair:
paulson@15234:      "[|summable f; 
paulson@15234:         \<forall>d. 0 < (f(n + (Suc(Suc 0) * d))) + f(n + ((Suc(Suc 0) * d) + 1))|]  
nipkow@15539:       ==> setsum f {0..<n} < suminf f"
paulson@14416: apply (drule summable_sums)
paulson@14416: apply (auto simp add: sums_def LIMSEQ_def)
paulson@15234: apply (drule_tac x = "f (n) + f (n + 1)" in spec)
paulson@15085: apply (auto iff: real_0_less_add_iff)
paulson@15085:    --{*legacy proof: not necessarily better!*}
paulson@14416: apply (rule_tac [2] ccontr, drule_tac [2] linorder_not_less [THEN iffD1])
paulson@14416: apply (frule_tac [2] no=no in sumr_pos_lt_pair_lemma) 
paulson@14416: apply (drule_tac x = 0 in spec, simp)
paulson@14416: apply (rotate_tac 1, drule_tac x = "Suc (Suc 0) * (Suc no) + n" in spec)
paulson@14416: apply (safe, simp)
nipkow@15539: apply (subgoal_tac "suminf f + (f (n) + f (n + 1)) \<le>
nipkow@15539:  setsum f {0 ..< Suc (Suc 0) * (Suc no) + n}")
nipkow@15539: apply (rule_tac [2] y = "setsum f {0..<n+ Suc (Suc 0)}" in order_trans)
paulson@14416: prefer 3 apply assumption
nipkow@15539: apply (rule_tac [2] y = "setsum f {0..<n} + (f (n) + f (n + 1))" in order_trans)
paulson@14416: apply simp_all 
nipkow@15539: apply (subgoal_tac "suminf f \<le> setsum f {0..< Suc (Suc 0) * (Suc no) + n}")
paulson@14416: apply (rule_tac [2] y = "suminf f + (f (n) + f (n + 1))" in order_trans)
nipkow@15539: prefer 3 apply simp
paulson@14416: apply (drule_tac [2] x = 0 in spec)
paulson@14416:  prefer 2 apply simp 
nipkow@15539: apply (subgoal_tac "0 \<le> setsum f {0 ..< Suc (Suc 0) * Suc no + n} + - suminf f")
nipkow@15539: apply (simp add: abs_if)
paulson@14416: apply (auto simp add: linorder_not_less [symmetric])
paulson@14416: done
paulson@14416: 
paulson@15085: text{*A summable series of positive terms has limit that is at least as
paulson@15085: great as any partial sum.*}
paulson@14416: 
paulson@14416: lemma series_pos_le: 
nipkow@15539:      "[| summable f; \<forall>m \<ge> n. 0 \<le> f(m) |] ==> setsum f {0..<n} \<le> suminf f"
paulson@14416: apply (drule summable_sums)
paulson@14416: apply (simp add: sums_def)
nipkow@15539: apply (cut_tac k = "setsum f {0..<n}" in LIMSEQ_const)
nipkow@15539: apply (erule LIMSEQ_le, blast)
nipkow@15539: apply (rule_tac x = n in exI, clarify)
nipkow@15539: apply (rule setsum_mono2)
nipkow@15539: apply auto
paulson@14416: done
paulson@14416: 
paulson@14416: lemma series_pos_less:
nipkow@15539:      "[| summable f; \<forall>m \<ge> n. 0 < f(m) |] ==> setsum f {0..<n} < suminf f"
nipkow@15539: apply (rule_tac y = "setsum f {0..<Suc n}" in order_less_le_trans)
paulson@14416: apply (rule_tac [2] series_pos_le, auto)
paulson@14416: apply (drule_tac x = m in spec, auto)
paulson@14416: done
paulson@14416: 
paulson@15085: text{*Sum of a geometric progression.*}
paulson@14416: 
nipkow@15539: lemma sumr_geometric:
nipkow@15539:  "x ~= 1 ==> (\<Sum>i=0..<n. x ^ i) = (x ^ n - 1) / (x - 1::real)"
paulson@15251: apply (induct "n", auto)
paulson@14416: apply (rule_tac c1 = "x - 1" in real_mult_right_cancel [THEN iffD1])
nipkow@15539: apply (auto simp add: mult_assoc left_distrib)
paulson@15234: apply (simp add: right_distrib diff_minus mult_commute)
paulson@14416: done
paulson@14416: 
paulson@14416: lemma geometric_sums: "abs(x) < 1 ==> (%n. x ^ n) sums (1/(1 - x))"
paulson@14416: apply (case_tac "x = 1")
paulson@15234: apply (auto dest!: LIMSEQ_rabs_realpow_zero2 
paulson@15234:         simp add: sumr_geometric sums_def diff_minus add_divide_distrib)
paulson@14416: apply (subgoal_tac "1 / (1 + -x) = 0/ (x - 1) + - 1/ (x - 1) ")
paulson@14416: apply (erule ssubst)
paulson@14416: apply (rule LIMSEQ_add, rule LIMSEQ_divide)
paulson@15234: apply (auto intro: LIMSEQ_const simp add: diff_minus minus_divide_right LIMSEQ_rabs_realpow_zero2)
paulson@14416: done
paulson@14416: 
paulson@15085: text{*Cauchy-type criterion for convergence of series (c.f. Harrison)*}
paulson@15085: 
nipkow@15539: lemma summable_convergent_sumr_iff:
nipkow@15539:  "summable f = convergent (%n. setsum f {0..<n})"
paulson@14416: by (simp add: summable_def sums_def convergent_def)
paulson@14416: 
paulson@14416: lemma summable_Cauchy:
paulson@14416:      "summable f =  
nipkow@15539:       (\<forall>e > 0. \<exists>N. \<forall>m \<ge> N. \<forall>n. abs(setsum f {m..<n}) < e)"
nipkow@15537: apply (auto simp add: summable_convergent_sumr_iff Cauchy_convergent_iff [symmetric] Cauchy_def diff_minus[symmetric])
nipkow@15539: apply (drule_tac [!] spec, auto)
paulson@14416: apply (rule_tac x = M in exI)
paulson@14416: apply (rule_tac [2] x = N in exI, auto)
paulson@14416: apply (cut_tac [!] m = m and n = n in less_linear, auto)
paulson@14416: apply (frule le_less_trans [THEN less_imp_le], assumption)
nipkow@15360: apply (drule_tac x = n in spec, simp)
paulson@14416: apply (drule_tac x = m in spec)
nipkow@15539: apply(simp add: setsum_diff[symmetric])
nipkow@15537: apply(subst abs_minus_commute)
nipkow@15539: apply(simp add: setsum_diff[symmetric])
nipkow@15539: apply(simp add: setsum_diff[symmetric])
paulson@14416: done
nipkow@15539: (* FIXME move ivl_ lemmas out of this theory *)
paulson@14416: 
paulson@15085: text{*Comparison test*}
paulson@15085: 
paulson@14416: lemma summable_comparison_test:
nipkow@15360:      "[| \<exists>N. \<forall>n \<ge> N. abs(f n) \<le> g n; summable g |] ==> summable f"
paulson@14416: apply (auto simp add: summable_Cauchy)
paulson@14416: apply (drule spec, auto)
paulson@14416: apply (rule_tac x = "N + Na" in exI, auto)
paulson@14416: apply (rotate_tac 2)
paulson@14416: apply (drule_tac x = m in spec)
paulson@14416: apply (auto, rotate_tac 2, drule_tac x = n in spec)
nipkow@15539: apply (rule_tac y = "\<Sum>k=m..<n. abs(f k)" in order_le_less_trans)
nipkow@15536: apply (rule setsum_abs)
nipkow@15539: apply (rule_tac y = "setsum g {m..<n}" in order_le_less_trans)
nipkow@15539: apply (auto intro: setsum_mono simp add: abs_interval_iff)
paulson@14416: done
paulson@14416: 
paulson@14416: lemma summable_rabs_comparison_test:
nipkow@15360:      "[| \<exists>N. \<forall>n \<ge> N. abs(f n) \<le> g n; summable g |] 
paulson@14416:       ==> summable (%k. abs (f k))"
paulson@14416: apply (rule summable_comparison_test)
paulson@14416: apply (auto simp add: abs_idempotent)
paulson@14416: done
paulson@14416: 
paulson@15085: text{*Limit comparison property for series (c.f. jrh)*}
paulson@15085: 
paulson@14416: lemma summable_le:
paulson@14416:      "[|\<forall>n. f n \<le> g n; summable f; summable g |] ==> suminf f \<le> suminf g"
paulson@14416: apply (drule summable_sums)+
paulson@14416: apply (auto intro!: LIMSEQ_le simp add: sums_def)
paulson@14416: apply (rule exI)
nipkow@15539: apply (auto intro!: setsum_mono)
paulson@14416: done
paulson@14416: 
paulson@14416: lemma summable_le2:
paulson@14416:      "[|\<forall>n. abs(f n) \<le> g n; summable g |]  
paulson@14416:       ==> summable f & suminf f \<le> suminf g"
paulson@14416: apply (auto intro: summable_comparison_test intro!: summable_le)
paulson@14416: apply (simp add: abs_le_interval_iff)
paulson@14416: done
paulson@14416: 
paulson@15085: text{*Absolute convergence imples normal convergence*}
paulson@14416: lemma summable_rabs_cancel: "summable (%n. abs (f n)) ==> summable f"
nipkow@15536: apply (auto simp add: summable_Cauchy)
paulson@14416: apply (drule spec, auto)
paulson@14416: apply (rule_tac x = N in exI, auto)
paulson@14416: apply (drule spec, auto)
nipkow@15539: apply (rule_tac y = "\<Sum>n=m..<n. abs(f n)" in order_le_less_trans)
nipkow@15536: apply (auto)
paulson@14416: done
paulson@14416: 
paulson@15085: text{*Absolute convergence of series*}
paulson@14416: lemma summable_rabs:
paulson@14416:      "summable (%n. abs (f n)) ==> abs(suminf f) \<le> suminf (%n. abs(f n))"
nipkow@15536: by (auto intro: LIMSEQ_le LIMSEQ_imp_rabs summable_rabs_cancel summable_sumr_LIMSEQ_suminf)
paulson@14416: 
paulson@14416: 
paulson@14416: subsection{* The Ratio Test*}
paulson@14416: 
paulson@14416: lemma rabs_ratiotest_lemma: "[| c \<le> 0; abs x \<le> c * abs y |] ==> x = (0::real)"
paulson@14416: apply (drule order_le_imp_less_or_eq, auto)
paulson@14416: apply (subgoal_tac "0 \<le> c * abs y")
paulson@14416: apply (simp add: zero_le_mult_iff, arith)
paulson@14416: done
paulson@14416: 
paulson@14416: lemma le_Suc_ex: "(k::nat) \<le> l ==> (\<exists>n. l = k + n)"
paulson@14416: apply (drule le_imp_less_or_eq)
paulson@14416: apply (auto dest: less_imp_Suc_add)
paulson@14416: done
paulson@14416: 
paulson@14416: lemma le_Suc_ex_iff: "((k::nat) \<le> l) = (\<exists>n. l = k + n)"
paulson@14416: by (auto simp add: le_Suc_ex)
paulson@14416: 
paulson@14416: (*All this trouble just to get 0<c *)
paulson@14416: lemma ratio_test_lemma2:
nipkow@15360:      "[| \<forall>n \<ge> N. abs(f(Suc n)) \<le> c*abs(f n) |]  
paulson@14416:       ==> 0 < c | summable f"
paulson@14416: apply (simp (no_asm) add: linorder_not_le [symmetric])
paulson@14416: apply (simp add: summable_Cauchy)
paulson@14416: apply (safe, subgoal_tac "\<forall>n. N \<le> n --> f (Suc n) = 0")
paulson@14416: prefer 2 apply (blast intro: rabs_ratiotest_lemma)
paulson@14416: apply (rule_tac x = "Suc N" in exI, clarify)
paulson@14416: apply (drule_tac n=n in Suc_le_imp_diff_ge2, auto) 
paulson@14416: done
paulson@14416: 
paulson@14416: lemma ratio_test:
nipkow@15360:      "[| c < 1; \<forall>n \<ge> N. abs(f(Suc n)) \<le> c*abs(f n) |]  
paulson@14416:       ==> summable f"
paulson@14416: apply (frule ratio_test_lemma2, auto)
paulson@15234: apply (rule_tac g = "%n. (abs (f N) / (c ^ N))*c ^ n" 
paulson@15234:        in summable_comparison_test)
paulson@14416: apply (rule_tac x = N in exI, safe)
paulson@14416: apply (drule le_Suc_ex_iff [THEN iffD1])
paulson@14416: apply (auto simp add: power_add realpow_not_zero)
nipkow@15539: apply (induct_tac "na", auto)
paulson@14416: apply (rule_tac y = "c*abs (f (N + n))" in order_trans)
paulson@14416: apply (auto intro: mult_right_mono simp add: summable_def)
paulson@14416: apply (simp add: mult_ac)
paulson@15234: apply (rule_tac x = "abs (f N) * (1/ (1 - c)) / (c ^ N)" in exI)
paulson@15234: apply (rule sums_divide) 
paulson@15234: apply (rule sums_mult) 
paulson@15234: apply (auto intro!: geometric_sums)
paulson@14416: done
paulson@14416: 
paulson@14416: 
paulson@15085: text{*Differentiation of finite sum*}
paulson@14416: 
paulson@14416: lemma DERIV_sumr [rule_format (no_asm)]:
paulson@14416:      "(\<forall>r. m \<le> r & r < (m + n) --> DERIV (%x. f r x) x :> (f' r x))  
nipkow@15539:       --> DERIV (%x. \<Sum>n=m..<n::nat. f n x) x :> (\<Sum>r=m..<n. f' r x)"
paulson@15251: apply (induct "n")
paulson@14416: apply (auto intro: DERIV_add)
paulson@14416: done
paulson@14416: 
paulson@14416: ML
paulson@14416: {*
paulson@14416: val sums_def = thm"sums_def";
paulson@14416: val summable_def = thm"summable_def";
paulson@14416: val suminf_def = thm"suminf_def";
paulson@14416: 
paulson@14416: val sumr_minus_one_realpow_zero = thm "sumr_minus_one_realpow_zero";
paulson@14416: val Suc_le_imp_diff_ge2 = thm "Suc_le_imp_diff_ge2";
paulson@14416: val sumr_one_lb_realpow_zero = thm "sumr_one_lb_realpow_zero";
paulson@14416: val sumr_group = thm "sumr_group";
paulson@14416: val sums_summable = thm "sums_summable";
paulson@14416: val summable_sums = thm "summable_sums";
paulson@14416: val summable_sumr_LIMSEQ_suminf = thm "summable_sumr_LIMSEQ_suminf";
paulson@14416: val sums_unique = thm "sums_unique";
paulson@14416: val series_zero = thm "series_zero";
paulson@14416: val sums_mult = thm "sums_mult";
paulson@14416: val sums_divide = thm "sums_divide";
paulson@14416: val sums_diff = thm "sums_diff";
paulson@14416: val suminf_mult = thm "suminf_mult";
paulson@14416: val suminf_mult2 = thm "suminf_mult2";
paulson@14416: val suminf_diff = thm "suminf_diff";
paulson@14416: val sums_minus = thm "sums_minus";
paulson@14416: val sums_group = thm "sums_group";
paulson@14416: val sumr_pos_lt_pair_lemma = thm "sumr_pos_lt_pair_lemma";
paulson@14416: val sumr_pos_lt_pair = thm "sumr_pos_lt_pair";
paulson@14416: val series_pos_le = thm "series_pos_le";
paulson@14416: val series_pos_less = thm "series_pos_less";
paulson@14416: val sumr_geometric = thm "sumr_geometric";
paulson@14416: val geometric_sums = thm "geometric_sums";
paulson@14416: val summable_convergent_sumr_iff = thm "summable_convergent_sumr_iff";
paulson@14416: val summable_Cauchy = thm "summable_Cauchy";
paulson@14416: val summable_comparison_test = thm "summable_comparison_test";
paulson@14416: val summable_rabs_comparison_test = thm "summable_rabs_comparison_test";
paulson@14416: val summable_le = thm "summable_le";
paulson@14416: val summable_le2 = thm "summable_le2";
paulson@14416: val summable_rabs_cancel = thm "summable_rabs_cancel";
paulson@14416: val summable_rabs = thm "summable_rabs";
paulson@14416: val rabs_ratiotest_lemma = thm "rabs_ratiotest_lemma";
paulson@14416: val le_Suc_ex = thm "le_Suc_ex";
paulson@14416: val le_Suc_ex_iff = thm "le_Suc_ex_iff";
paulson@14416: val ratio_test_lemma2 = thm "ratio_test_lemma2";
paulson@14416: val ratio_test = thm "ratio_test";
paulson@14416: val DERIV_sumr = thm "DERIV_sumr";
paulson@14416: *}
paulson@14416: 
paulson@14416: end