Library Interval.Poly.Taylor_poly
This file is part of the CoqApprox formalization of rigorous
polynomial approximation in Coq:
http://tamadi.gforge.inria.fr/CoqApprox/
Copyright (C) 2010-2012, ENS de Lyon.
Copyright (C) 2010-2016, Inria.
Copyright (C) 2014-2016, IRIT.
This library is governed by the CeCILL-C license under French law and
abiding by the rules of distribution of free software. You can use,
modify and/or redistribute the library under the terms of the CeCILL-C
license as circulated by CEA, CNRS and Inria at the following URL:
http://www.cecill.info/
As a counterpart to the access to the source code and rights to copy,
modify and redistribute granted by the license, users are provided
only with a limited warranty and the library's author, the holder of
the economic rights, and the successive licensors have only limited
liability. See the COPYING file for more details.
From Coq Require Import ZArith Reals.
From Flocq Require Import Raux.
From mathcomp.ssreflect Require Import ssreflect ssrfun ssrbool eqtype ssrnat seq fintype bigop.
Require Import Interval.
Require Import Datatypes Basic_rec.
Set Implicit Arguments.
Module TaylorPoly (C : FullOps) (P : PolyOps C).
Needs functions defining the recurrences, as well as rec1, rec2, grec1.
Definition cst_rec (x : C.T) (n : nat) := C.mask C.zero x.
Definition var_rec (a b : C.T) (n : nat) := C.mask (C.mask C.zero a) b.
Definition T_cst c (x : C.T) := P.rec1 cst_rec (C.mask c x).
Note that in addition to the Taylor expansion point that is
the 2nd parameter of T_cst, the first one is the value of
the constant itself.
Definition T_var x := P.rec2 var_rec x (C.mask C.one x).
Section PrecIsPropagated1.
Variable u : C.U.
Definition inv_rec (x : C.T) (a : C.T) (n : nat) : C.T := C.div u a (C.opp x).
Definition exp_rec (a : C.T) (n : nat) : C.T := C.div u a (C.from_nat u n).
Definition sin_rec (a b : C.T) (n : nat) : C.T :=
C.div u (C.opp a) (C.mul u (C.from_nat u n) (C.from_nat u n.-1)).
Definition cos_rec (a b : C.T) (n : nat) : C.T :=
C.div u (C.opp a) (C.mul u (C.from_nat u n) (C.from_nat u n.-1)).
Definition pow_aux_rec (p : Z) (x : C.T) (_ : C.T) (n : nat)
:= if Z.ltb p Z0 || Z.geb p (Z.of_nat n) then
C.power_int u x (p - Z.of_nat n)%Z
else C.mask C.zero x.
Definition sqrt_rec (x : C.T) (a : C.T) (n : nat) :=
let nn := C.from_nat u n in
let n1 := C.from_nat u n.-1 in
let two := C.from_nat u 2 in
(C.one - two × n1) × a / (two × x × nn).
Definition invsqrt_rec (x : C.T) (a : C.T) (n : nat) :=
let nn := C.from_nat u n in
let n1 := C.from_nat u n.-1 in
let two := C.from_nat u 2 in
C.opp (C.one + two × n1) × a / (two × x × nn).
End PrecIsPropagated1.
Section PrecIsPropagated2.
Variable u : P.U.
Definition T_inv x := P.rec1 (inv_rec u x) (C.inv u x).
Definition T_exp x := P.rec1 (exp_rec u) (C.exp u x).
Definition T_sin x := P.rec2 (sin_rec u) (C.sin u x) (C.cos u x).
Definition T_cos x := P.rec2 (cos_rec u) (C.cos u x) (C.opp (C.sin u x)).
Definition T_sqrt x := P.rec1 (sqrt_rec u x) (C.sqrt u x).
Definition T_invsqrt x := P.rec1 (invsqrt_rec u x) (C.invsqrt u x).
Definition T_power_int (p : Z) x (n : nat) :=
P.dotmuldiv u (falling_seq p n) (fact_seq n)
(P.rec1 (pow_aux_rec u p x) (C.power_int u x p) n).
Definition T_tan x :=
let polyX := P.lift 1 P.one in
let J := C.tan u x in
let s := [::] in
let F q n :=
let q' := P.deriv u q in
P.div_mixed_r u (P.add u q' (P.lift 2 q')) (C.from_nat u n) in
let G q _ := P.horner u q J in
P.grec1 F G polyX s.
Definition T_atan x :=
let q1 := P.one in
let J := C.atan u x in
let s := [:: J] in
let F q n :=
let q2nX := P.mul_mixed u (C.from_nat u ((n.-1).*2)) (P.lift 1 q) in
let q' := P.deriv u q in
P.div_mixed_r u (P.sub u (P.add u q' (P.lift 2 q')) q2nX) (C.from_nat u n) in
let G q n :=
C.div u (P.horner u q x)
(C.power_int u (C.add u C.one (C.sqr u x)) (Z_of_nat n)) in
P.grec1 F G q1 s.
Definition T_ln x n :=
let lg := C.ln u x in
let y := C.mask x lg in
P.polyCons lg
(if n is n'.+1 then
let p1 := (-1)%Z in
P.dotmuldiv u (falling_seq p1 n') (behead (fact_seq n))
(P.rec1 (pow_aux_rec u p1 y) (C.power_int u y p1) n')
else P.polyNil).
End PrecIsPropagated2.
End TaylorPoly.