src/HOL/Analysis/Norm_Arith.thy

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(*  Title:      HOL/Analysis/Norm_Arith.thy
    Author:     Amine Chaieb, University of Cambridge
*)

section \<open>Linear Decision Procedure for Normed Spaces\<close>

theory Norm_Arith
imports "HOL-Library.Sum_of_Squares"
begin

(* FIXME: move elsewhere *)
lemma sum_sqs_eq:
  fixes x::"'a::idom" shows "x * x + y * y = x * (y * 2) \<Longrightarrow> y = x"
  by algebra

lemma norm_cmul_rule_thm:
  fixes x :: "'a::real_normed_vector"
  shows "b \<ge> norm x \<Longrightarrow> \<bar>c\<bar> * b \<ge> norm (scaleR c x)"
  unfolding norm_scaleR
  apply (erule mult_left_mono)
  apply simp
  done

(* FIXME: Move all these theorems into the ML code using lemma antiquotation *)
lemma norm_add_rule_thm:
  fixes x1 x2 :: "'a::real_normed_vector"
  shows "norm x1 \<le> b1 \<Longrightarrow> norm x2 \<le> b2 \<Longrightarrow> norm (x1 + x2) \<le> b1 + b2"
  by (rule order_trans [OF norm_triangle_ineq add_mono])

lemma ge_iff_diff_ge_0:
  fixes a :: "'a::linordered_ring"
  shows "a \<ge> b \<equiv> a - b \<ge> 0"
  by (simp add: field_simps)

lemma pth_1:
  fixes x :: "'a::real_normed_vector"
  shows "x \<equiv> scaleR 1 x" by simp

lemma pth_2:
  fixes x :: "'a::real_normed_vector"
  shows "x - y \<equiv> x + -y"
  by (atomize (full)) simp

lemma pth_3:
  fixes x :: "'a::real_normed_vector"
  shows "- x \<equiv> scaleR (-1) x"
  by simp

lemma pth_4:
  fixes x :: "'a::real_normed_vector"
  shows "scaleR 0 x \<equiv> 0"
    and "scaleR c 0 = (0::'a)"
  by simp_all

lemma pth_5:
  fixes x :: "'a::real_normed_vector"
  shows "scaleR c (scaleR d x) \<equiv> scaleR (c * d) x"
  by simp

lemma pth_6:
  fixes x :: "'a::real_normed_vector"
  shows "scaleR c (x + y) \<equiv> scaleR c x + scaleR c y"
  by (simp add: scaleR_right_distrib)

lemma pth_7:
  fixes x :: "'a::real_normed_vector"
  shows "0 + x \<equiv> x"
    and "x + 0 \<equiv> x"
  by simp_all

lemma pth_8:
  fixes x :: "'a::real_normed_vector"
  shows "scaleR c x + scaleR d x \<equiv> scaleR (c + d) x"
  by (simp add: scaleR_left_distrib)

lemma pth_9:
  fixes x :: "'a::real_normed_vector"
  shows "(scaleR c x + z) + scaleR d x \<equiv> scaleR (c + d) x + z"
    and "scaleR c x + (scaleR d x + z) \<equiv> scaleR (c + d) x + z"
    and "(scaleR c x + w) + (scaleR d x + z) \<equiv> scaleR (c + d) x + (w + z)"
  by (simp_all add: algebra_simps)

lemma pth_a:
  fixes x :: "'a::real_normed_vector"
  shows "scaleR 0 x + y \<equiv> y"
  by simp

lemma pth_b:
  fixes x :: "'a::real_normed_vector"
  shows "scaleR c x + scaleR d y \<equiv> scaleR c x + scaleR d y"
    and "(scaleR c x + z) + scaleR d y \<equiv> scaleR c x + (z + scaleR d y)"
    and "scaleR c x + (scaleR d y + z) \<equiv> scaleR c x + (scaleR d y + z)"
    and "(scaleR c x + w) + (scaleR d y + z) \<equiv> scaleR c x + (w + (scaleR d y + z))"
  by (simp_all add: algebra_simps)

lemma pth_c:
  fixes x :: "'a::real_normed_vector"
  shows "scaleR c x + scaleR d y \<equiv> scaleR d y + scaleR c x"
    and "(scaleR c x + z) + scaleR d y \<equiv> scaleR d y + (scaleR c x + z)"
    and "scaleR c x + (scaleR d y + z) \<equiv> scaleR d y + (scaleR c x + z)"
    and "(scaleR c x + w) + (scaleR d y + z) \<equiv> scaleR d y + ((scaleR c x + w) + z)"
  by (simp_all add: algebra_simps)

lemma pth_d:
  fixes x :: "'a::real_normed_vector"
  shows "x + 0 \<equiv> x"
  by simp

lemma norm_imp_pos_and_ge:
  fixes x :: "'a::real_normed_vector"
  shows "norm x \<equiv> n \<Longrightarrow> norm x \<ge> 0 \<and> n \<ge> norm x"
  by atomize auto

lemma real_eq_0_iff_le_ge_0:
  fixes x :: real
  shows "x = 0 \<equiv> x \<ge> 0 \<and> - x \<ge> 0"
  by arith

lemma norm_pths:
  fixes x :: "'a::real_normed_vector"
  shows "x = y \<longleftrightarrow> norm (x - y) \<le> 0"
    and "x \<noteq> y \<longleftrightarrow> \<not> (norm (x - y) \<le> 0)"
  using norm_ge_zero[of "x - y"] by auto

lemmas arithmetic_simps =
  arith_simps
  add_numeral_special
  add_neg_numeral_special
  mult_1_left
  mult_1_right

ML_file \<open>normarith.ML\<close>

method_setup\<^marker>\<open>tag important\<close> norm = \<open>
  Scan.succeed (SIMPLE_METHOD' o NormArith.norm_arith_tac)
\<close> "prove simple linear statements about vector norms"


text \<open>Hence more metric properties.\<close>
text\<^marker>\<open>tag important\<close> \<open>%whitespace\<close>
proposition dist_triangle_add:
  fixes x y x' y' :: "'a::real_normed_vector"
  shows "dist (x + y) (x' + y') \<le> dist x x' + dist y y'"
  by norm

lemma dist_triangle_add_half:
  fixes x x' y y' :: "'a::real_normed_vector"
  shows "dist x x' < e / 2 \<Longrightarrow> dist y y' < e / 2 \<Longrightarrow> dist(x + y) (x' + y') < e"
  by norm

end