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quaternion.v
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quaternion.v
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(* coq-robot (c) 2017 AIST and INRIA. License: LGPL-2.1-or-later. *)
From HB Require Import structures.
Require Import NsatzTactic.
From mathcomp Require Import all_ssreflect ssralg ssrint ssrnum rat poly.
From mathcomp Require Import closed_field polyrcf matrix mxalgebra mxpoly zmodp.
From mathcomp Require Import realalg complex fingroup perm.
From mathcomp Require Import interval reals trigo.
Require Import ssr_ext euclidean vec_angle frame rot.
From mathcomp.analysis Require Import forms.
Require Import extra_trigo.
(******************************************************************************)
(* Quaternions *)
(* *)
(* This file develops the theory of quaternions. It defines the type of *)
(* quaternions and the type of unit quaternions and show that quaternions *)
(* form a ZmodType, a RingType, a LmodType, a UnitRingType. It also defines *)
(* polar coordinates and dual quaternions. *)
(* *)
(* quat R == type of quaternions over the ringType R *)
(* x%:q == quaternion with scalar part x and vector part 0 *)
(* x \is realq == the quaternion x has no vector part *)
(* u%:v == pure quaternion (or vector quaternion) with scalar part 0 *)
(* and vector part u *)
(* x \is pureq == the quaternion x has no scalar part *)
(* `i, `j, `k == basic quaternions *)
(* x.1 == scalar part of the quaternion x *)
(* x.2 == vector part of the quaternion x *)
(* x^*q == conjugate of quaternion x *)
(* normq x == norm of the quaternion x *)
(* uquat R == type of unit quaternions, i.e., quaternions with norm 1 *)
(* conjugation x == v |-> x v x^* *)
(* *)
(* Polar coordinates: *)
(* polar_of_quat a == polar coordinates of the quaternion a *)
(* quat_of_polar a u == quaternion corresponding to the polar coordinates *)
(* angle a and vector u *)
(* quat_rot x == snd \o conjugation x (rotation of angle 2a about *)
(* vector v where a,v are the polar coordinates of x, *)
(* a unit quaternion *)
(* Dual numbers: *)
(* dual R == the type of dual numbers over a ringType R *)
(* x.1 == left part of the dual number x *)
(* x.2 == right part of the dual number x *)
(* Dual numbers are equipped with a structure of ZmodType, RingType, and of *)
(* LmodType when R is a ringType, of Com/UnitRingType when R is a *)
(* Com/UnitRingType. *)
(* *)
(* Dual quaternions: *)
(* x +ɛ* y == dual number formed by x and y *)
(* dquat == type of dual quaternions *)
(* x \is puredq == the dual quaternion x is pure *)
(* a \is dnum == a has no vector part *)
(* x^*dq == conjugate of dual quaternion x *)
(* *)
(******************************************************************************)
Reserved Notation "x %:q" (at level 2, format "x %:q").
Reserved Notation "x %:v" (at level 2, format "x %:v").
Reserved Notation "x '_i'" (at level 1, format "x '_i'").
Reserved Notation "x '_j'" (at level 1, format "x '_j'").
Reserved Notation "x '_k'" (at level 1, format "x '_k'").
Reserved Notation "'`i'".
Reserved Notation "'`j'".
Reserved Notation "'`k'".
Reserved Notation "x '^*q'" (at level 2, format "x '^*q'").
Reserved Notation "r *`i" (at level 3).
Reserved Notation "r *`j" (at level 3).
Reserved Notation "r *`k" (at level 3).
Reserved Notation "x +ɛ* y"
(at level 40, left associativity, format "x +ɛ* y").
Reserved Notation "x -ɛ* y"
(at level 40, left associativity, format "x -ɛ* y").
Reserved Notation "x '^*d'" (at level 2, format "x '^*d'").
Reserved Notation "x '^*dq'" (at level 2, format "x '^*dq'").
Declare Scope quat_scope.
Declare Scope dual_scope.
Set Implicit Arguments.
Unset Strict Implicit.
Unset Printing Implicit Defensive.
Local Open Scope ring_scope.
Import Order.TTheory GRing.Theory Num.Def Num.Theory.
(* TODO: overrides forms.v *)
Notation "u '``_' i" := (u (@GRing.zero _) i) : ring_scope.
Section quaternion0.
Variable R : ringType.
Record quat := mkQuat {quatl : R ; quatr : 'rV[R]_3 }.
Implicit Types x y : quat.
Local Notation "x %:q" := (mkQuat x 0).
Local Notation "x %:v" := (mkQuat 0 x).
Local Notation "'`i'" := ('e_0)%:v.
Local Notation "'`j'" := ('e_1)%:v.
Local Notation "'`k'" := ('e_2%:R)%:v.
Local Notation "x '_i'" := ((x.2)``_0).
Local Notation "x '_j'" := ((x.2)``_1).
Local Notation "x '_k'" := ((x.2)``_(2%:R : 'I_3)).
Coercion pair_of_quat x := let: mkQuat x1 x2 := x in (x1, x2).
Let quat_of_pair (a : R * 'rV[R]_3) := let: (a1, a2) := a in mkQuat a1 a2.
Lemma quat_of_pairK : cancel pair_of_quat quat_of_pair.
Proof. by case. Qed.
HB.instance Definition _ := Equality.copy quat (can_type quat_of_pairK).
HB.instance Definition _ := Choice.copy quat (can_type quat_of_pairK).
Lemma eq_quat x y : (x == y) = (x.1 == y.1) && (x.2 == y.2).
Proof.
case: x y => [? ?] [? ?] /=.
apply/idP/idP => [/eqP [ -> ->]|/andP[/eqP -> /eqP -> //]]; by rewrite !eqxx.
Qed.
Definition addq x y := nosimpl (mkQuat (x.1 + y.1) (x.2 + y.2)).
Lemma addqC : commutative addq.
Proof. move=> *; congr mkQuat; by rewrite addrC. Qed.
Lemma addqA : associative addq.
Proof. move=> *; congr mkQuat; by rewrite addrA. Qed.
Lemma add0q : left_id 0%:q addq.
Proof. case=> *; by rewrite /addq /= 2!add0r. Qed.
Definition oppq x := nosimpl (mkQuat (- x.1) (- x.2)).
Lemma addNq : left_inverse 0%:q oppq addq.
Proof. move=> *; congr mkQuat; by rewrite addNr. Qed.
HB.instance Definition _ := @GRing.isZmodule.Build quat _ _ _ addqA addqC add0q addNq.
Lemma addqE x y : x + y = addq x y. Proof. by []. Qed.
Lemma oppqE x : - x = oppq x. Proof. by []. Qed.
Local Notation "r *`i" := (mkQuat 0 (r *: 'e_0)).
Local Notation "r *`j" := (mkQuat 0 (r *: 'e_1)).
Local Notation "r *`k" := (mkQuat 0 (r *: 'e_2%:R)).
Lemma quatE x : x = x.1%:q + x.2%:v.
Proof. by apply/eqP; rewrite eq_quat /=; Simp.r. Qed.
Lemma quatrE x : x.2%:v = x _i *`i + x _j *`j + x _k *`k.
Proof. by apply/eqP; rewrite eq_quat /=; Simp.r; rewrite -vec3E. Qed.
Lemma quat_scalarE (r s : R) : (r%:q == s%:q) = (r == s).
Proof. by apply/idP/idP => [/eqP[] ->|/eqP -> //]. Qed.
Lemma quat_realN (r : R) : (- r)%:q = - (r%:q).
Proof. by rewrite oppqE /oppq /= oppr0. Qed.
Lemma quat_vectN (u : 'rV[R]_3) : (- u)%:v = - (u%:v).
Proof. by rewrite oppqE /oppq /= oppr0. Qed.
Lemma quat_realD (r s : R) : (r + s)%:q = r%:q + s%:q.
Proof. by rewrite addqE /addq /= add0r. Qed.
Lemma quat_vectD (u v : 'rV[R]_3) : (u + v)%:v = u%:v + v%:v.
Proof. by rewrite addqE /addq /= addr0. Qed.
Lemma quat_realB (r s : R) : (r - s)%:q = r%:q - s%:q.
Proof. by rewrite quat_realD quat_realN. Qed.
Lemma quat_vectB (u v : 'rV[R]_3) : (u - v)%:v = u%:v - v%:v.
Proof. by rewrite quat_vectD quat_vectN. Qed.
Definition pureq := [qualify x : quat | x.1 == 0].
Fact pureq_key : pred_key pureq. Proof. by []. Qed.
Canonical pureq_keyed := KeyedQualifier pureq_key.
Definition realq := [qualify x : quat | x.2 == 0].
Fact realq_key : pred_key realq. Proof. by []. Qed.
Canonical realq_keyed := KeyedQualifier realq_key.
End quaternion0.
Delimit Scope quat_scope with quat.
Local Open Scope quat_scope.
Notation "r %:q" := (mkQuat r 0) : quat_scope.
Notation "u %:v" := (mkQuat 0 u) : quat_scope.
Notation "'`i'" := ('e_0)%:v : quat_scope.
Notation "'`j'" := ('e_1)%:v : quat_scope.
Notation "'`k'" := ('e_2%:R)%:v : quat_scope.
Notation "x '_i'" := ((x.2)``_0) : quat_scope.
Notation "x '_j'" := ((x.2)``_1) : quat_scope.
Notation "x '_k'" := ((x.2)``_(2%:R : 'I_3)) : quat_scope.
Notation "r *`i" := (mkQuat 0 (r *: 'e_0)) : quat_scope.
Notation "r *`j" := (mkQuat 0 (r *: 'e_1)) : quat_scope.
Notation "r *`k" := (mkQuat 0 (r *: 'e_2%:R)) : quat_scope.
Arguments pureq {R}.
Section quaternion.
Variable R : comRingType.
Implicit Types x y : quat R.
Definition mulq x y := nosimpl
(mkQuat (x.1 * y.1 - x.2 *d y.2) (x.1 *: y.2 + y.1 *: x.2 + x.2 *v y.2)).
Lemma mulqA : associative mulq.
Proof.
move=> [a a'] [b b'] [c c']; congr mkQuat => /=.
- rewrite mulrDr mulrDl mulrA -!addrA; congr (_ + _).
rewrite mulrN !dotmulDr !dotmulDl !opprD !addrA dot_crossmulC; congr (_ + _).
rewrite addrC addrA; congr (_ + _ + _).
by rewrite mulrC dotmulvZ mulrN.
by rewrite dotmulZv.
by rewrite dotmulvZ dotmulZv.
- rewrite 2![in LHS]scalerDr 1![in RHS]scalerDl scalerA.
rewrite -4![in LHS]addrA -3![in RHS]addrA; congr (_ + _).
rewrite [in RHS]scalerDr [in RHS]addrCA
-[in RHS]addrA -[in LHS]addrA; congr (_ + _).
by rewrite scalerA mulrC -scalerA.
rewrite [in RHS]scalerDr [in LHS]scalerDl [in LHS]addrCA
-[in RHS]addrA -addrA; congr (_ + _).
by rewrite scalerA mulrC.
rewrite (addrC (a *: _)) linearD /= (addrC (a' *v _)) linearD /=.
rewrite -![in LHS]addrA ![in LHS]addrA (addrC (- _ *: a'))
-![in LHS]addrA; congr (_ + _).
by rewrite linearZ.
rewrite [in RHS](@lieC _ (vec3 R)) /= linearD /= opprD [in RHS]addrCA
![in LHS]addrA addrC -[in LHS]addrA.
congr (_ + _); first by rewrite linearZ /= (@lieC _ (vec3 R)) scalerN.
rewrite addrA addrC linearD /= opprD [in RHS]addrCA; congr (_ + _).
by rewrite !linearZ /= (@lieC _ (vec3 R)).
rewrite 2!double_crossmul opprD opprK
[in RHS]addrC addrA; congr (_ + _); last first.
by rewrite scaleNr.
by rewrite dotmulC scaleNr; congr (_ + _); rewrite dotmulC.
Qed.
Lemma mul1q : left_id 1%:q mulq.
Proof.
case=> a a'; rewrite /mulq /=; congr mkQuat; Simp.r => /=.
by rewrite dotmul0v subr0.
by rewrite linear0l addr0.
Qed.
Lemma mulq1 : right_id 1%:q mulq.
Proof.
case=> a a'; rewrite /mulq /=; congr mkQuat; Simp.r => /=.
by rewrite dotmulv0 subr0.
by rewrite linear0r addr0.
Qed.
Lemma mulqDl : left_distributive mulq (@addq R).
Proof.
move=> [a a'] [b b'] [c c']; rewrite /mulq /=; congr mkQuat => /=.
by rewrite [in RHS]addrCA 2!addrA -mulrDl (addrC a) dotmulDl opprD addrA.
rewrite scalerDl -!addrA; congr (_ + _).
rewrite [in RHS](addrCA (a' *v c')) [in RHS](addrCA (c *: a')); congr (_ + _).
rewrite scalerDr -addrA; congr (_ + _).
rewrite addrCA; congr (_ + _).
by rewrite (@lieC _ (vec3 R))/= linearD /= (@lieC _ (vec3 R)) opprD opprK (@lieC _ (vec3 R) b').
Qed.
Lemma mulqDr : right_distributive mulq (@addq R).
Proof.
move=> [a a'] [b b'] [c c']; rewrite /mulq /=; congr mkQuat => /=.
rewrite mulrDr -!addrA; congr (_ + _).
rewrite addrCA; congr (_ + _).
by rewrite dotmulDr opprD.
rewrite scalerDr -!addrA; congr (_ + _).
rewrite [in RHS](addrCA (a' *v b')) [in RHS](addrCA (b *: a')); congr (_ + _).
rewrite scalerDl -addrA; congr (_ + _).
by rewrite addrCA linearD.
Qed.
Lemma oneq_neq0 : 1%:q != 0 :> quat R.
Proof. apply/eqP => -[]; apply/eqP. exact: oner_neq0. Qed.
HB.instance Definition _ := @GRing.Zmodule_isRing.Build (quat R) _ _ mulqA mul1q mulq1 mulqDl mulqDr oneq_neq0.
Lemma mulqE x y : x * y = mulq x y. Proof. by []. Qed.
Lemma realq_comm x y : x \is realq R -> x * y = y * x.
Proof.
rewrite qualifE; move: x y => [x1 x2] [y1 y2] /= /eqP->.
congr mkQuat => /=; first by rewrite dotmul0v dotmulv0 mulrC.
by rewrite scaler0 !linear0 add0r addr0 -/(crossmulr _ _) linear0 addr0.
Qed.
Lemma realq_real (r : R) : r%:q \is realq R.
Proof. by rewrite qualifE. Qed.
Lemma realqE x : x \is realq R -> x = (x.1)%:q.
Proof. by rewrite qualifE; case: x => [x1 x2] /= /eqP->. Qed.
Lemma quat_realM (r s : R) : (r * s)%:q = r%:q * s%:q.
Proof. by congr mkQuat; rewrite /= (dotmul0v, linear0l); Simp.r. Qed.
Lemma iiN1 : `i * `i = -1.
Proof. by congr mkQuat; rewrite (dote2, @liexx _ (vec3 R)) /=; Simp.r. Qed.
Lemma ijk : `i * `j = `k.
Proof. by congr mkQuat; rewrite /= (dote2, vecij); Simp.r. Qed.
Lemma ikNj : `i * `k = - `j.
Proof. by congr mkQuat; rewrite /= (dote2, vecik); Simp.r. Qed.
Lemma jiNk : `j * `i = - `k.
Proof. by congr mkQuat; rewrite /= (dote2, vecji); Simp.r. Qed.
Lemma jjN1 : `j * `j = -1.
Proof. by congr mkQuat; rewrite /= (dote2, @liexx _ (vec3 R)); Simp.r. Qed.
Lemma jkNi : `j * `k = `i.
Proof. by congr mkQuat; rewrite /= ?(dote2, vecjk) //; Simp.r. Qed.
Lemma kij : `k * `i = `j.
Proof. by congr mkQuat; rewrite /= (dote2, vecki); Simp.r. Qed.
Lemma kjNi : `k * `j = - `i.
Proof. by congr mkQuat; rewrite /= (dote2, veckj); Simp.r. Qed.
Lemma kkN1 : `k * `k = -1.
Proof. by congr mkQuat; rewrite /= (dote2, @liexx _ (vec3 R)); Simp.r. Qed.
Definition scaleq k x := mkQuat (k * x.1) (k *: x.2).
Lemma scaleqA r s x : scaleq r (scaleq s x) = scaleq (r * s) x.
Proof.
rewrite /scaleq /=; congr mkQuat; by [rewrite mulrA | rewrite scalerA].
Qed.
Lemma scaleq1 : left_id 1 scaleq.
Proof.
by move=> q; rewrite /scaleq mul1r scale1r; apply/eqP; rewrite eq_quat /= !eqxx.
Qed.
Lemma scaleqDr : @right_distributive R (quat R) scaleq +%R.
Proof. move=> a b c; by rewrite /scaleq /= mulrDr scalerDr. Qed.
Lemma scaleqDl x : {morph (scaleq^~ x : R -> quat R) : r s / r + s}.
Proof. by move=> r s; rewrite /scaleq mulrDl /= scalerDl; congr mkQuat. Qed.
HB.instance Definition _ := @GRing.Zmodule_isLmodule.Build _ (quat R) scaleq scaleqA scaleq1 scaleqDr scaleqDl.
Lemma scaleqE (k : R) x : k *: x = k *: x.1%:q + k *: x.2%:v.
Proof. by apply/eqP; rewrite eq_quat /=; Simp.r. Qed.
Lemma quat_realZ (k : R) (r : R) : (k * r)%:q = k *: r%:q.
Proof. by congr mkQuat; rewrite scaler0. Qed.
Lemma quat_vectZ (k : R) (u : 'rV[R]_3) : (k *: u)%:v = k *: u%:v.
Proof. by congr mkQuat; rewrite /= mulr0. Qed.
Lemma quatAl k x y : k *: (x * y) = k *: x * y.
Proof.
case: x y => [x1 x2] [y1 y2]; apply/eqP.
rewrite !mulqE /mulq /= scaleqE /= eq_quat /=.
apply/andP; split; first by Simp.r; rewrite mulrBr mulrA dotmulZv.
apply/eqP; Simp.r; rewrite 2!scalerDr scalerA -2!addrA; congr (_ + _).
by rewrite linearZl_LR /=; congr (_ + _); rewrite scalerA mulrC -scalerA.
Qed.
HB.instance Definition _ := @GRing.Lmodule_isLalgebra.Build R (quat R) quatAl.
Lemma quatAr k x y : k *: (x * y) = x * (k *: y).
Proof.
case: x y => [x1 x2] [y1 y2]; apply/eqP.
rewrite !mulqE /mulq /= scaleqE /= eq_quat /=.
apply/andP; split; first by Simp.r; rewrite /= mulrBr mulrCA mulrA dotmulvZ.
apply/eqP; Simp.r; rewrite 2!scalerDr !scalerA.
rewrite (mulrC k); congr (_ + _ + _).
by rewrite linearZr_LR/=.
Qed.
HB.instance Definition _ := @GRing.Lalgebra_isAlgebra.Build _ (quat R) quatAr.
Lemma quat_algE r : r%:q = r%:A.
Proof. by apply/eqP; rewrite eq_quat //=; Simp.r. Qed.
Definition conjq x := nosimpl (mkQuat x.1 (- x.2)).
Local Notation "x '^*q'" := (conjq x).
Lemma conjq_def x : x^*q = mkQuat x.1 (- x.2).
Proof. by case: x. Qed.
Lemma conjq_linear : linear conjq.
Proof.
move=> k /= x y; rewrite !conjq_def /= scaleqE addqE /addq /=; Simp.r.
by rewrite linearN /= linearD.
Qed.
HB.instance Definition _ := @GRing.isLinear.Build _ (quat R) _ _ conjq conjq_linear.
Lemma conjqI x : (x ^*q) ^*q = x.
Proof. by rewrite conjq_def; case: x => x1 x2 /=; rewrite opprK. Qed.
Lemma conjq0 : (0%:v)^*q = 0.
Proof. by rewrite conjq_def oppr0. Qed.
Lemma conjq_comm x : x^*q * x = x * x^*q.
Proof.
apply/eqP; rewrite eq_quat /=.
do ! rewrite (linearNl,linearNr,(@liexx _ (vec3 R)),dotmulvN,dotmulNv,subr0,opprK,
scaleNr,scalerN,eqxx) /=.
by rewrite addrC.
Qed.
Lemma conjq_addMC x y : x * y + (x * y)^*q = y * x + (y * x) ^*q.
Proof.
case: x => x1 x2; case: y => y1 y2; congr mkQuat => /=.
by rewrite [y1 * _]mulrC [y2 *d _]dotmulC.
rewrite !opprD !addrA [_ + x1 *:y2]addrC -!addrA; congr (_ + (_ + _)).
by rewrite [LHS]addrC [RHS]addrC !addrA !subrK addrC.
Qed.
Lemma realq_conjD x : x + x^*q \is realq R.
Proof. by case: x => x1 x2; rewrite addqE /addq /= subrr qualifE. Qed.
Lemma realq_conjM x : x * x^*q \is realq R.
Proof.
case: x => [x1 x2]; rewrite mulqE /mulq /= scalerN linearN /=.
rewrite opprK [- _ + _]addrC subrr add0r.
rewrite linearN/= (@liexx _ (vec3 R)) oppr0.
by rewrite qualifE.
Qed.
Lemma conjq_comm2 x y : y^*q * x + x^*q * y = x * y^*q + y * x^*q.
Proof.
apply: (addIr (x * x ^*q + y * y ^*q)).
rewrite [RHS]addrAC !addrA -mulrDr -[RHS]addrA -mulrDr -mulrDl -linearD /=.
rewrite addrC !addrA -conjq_comm -mulrDr -addrA -conjq_comm -mulrDr -mulrDl.
by rewrite -linearD /= [y + x]addrC conjq_comm.
Qed.
Lemma conjqM x y : (x * y)^*q = y^*q * x^*q.
Proof.
case: x y => [x1 x2] [y1 y2] /=.
rewrite 2!conjq_def /= mulqE /mulq /= mulrC dotmulC dotmulvN dotmulNv opprK;
congr mkQuat.
rewrite 2!opprD.
rewrite (addrC (- (x1 *: y2))).
congr (_ + _ + _).
- by rewrite scalerN.
- by rewrite scalerN.
- rewrite linearN/= (@lieC _ (vec3 R) x2)/= opprK.
rewrite -(@lieC _ (vec3 R) x2)/= linearN/=.
by rewrite (@lieC _ (vec3 R) x2)/= opprK.
Qed.
Lemma quat_realC (r : R) : (r%:q)^*q = r%:q.
Proof. by congr mkQuat; rewrite /= oppr0. Qed.
Lemma quat_vectC (u : 'rV_3) : (u%:v)^*q = -(u%:v).
Proof. by congr mkQuat; rewrite /= oppr0. Qed.
End quaternion.
Arguments pureq {R}.
Arguments realq {R}.
Notation "x '^*q'" := (conjq x) : quat_scope.
Section quaternion1.
Variable R : realType.
Implicit Types x y : quat R.
Definition sqrq x := x.1 ^+ 2 + norm (x.2) ^+ 2.
Lemma sqrq0 : sqrq 0 = 0. Proof. by rewrite /sqrq norm0 expr0n add0r. Qed.
Lemma sqrq_ge0 x : 0 <= sqrq x. Proof. by rewrite addr_ge0 // sqr_ge0. Qed.
Lemma sqrq_eq0 x : (sqrq x == 0) = (x == 0).
Proof.
rewrite /sqrq paddr_eq0 ?sqr_ge0// !sqrf_eq0 norm_eq0 -xpair_eqE.
by rewrite -surjective_pairing.
Qed.
Lemma sqrqN x : sqrq (- x) = sqrq x.
Proof. by rewrite /sqrq /= normN sqrrN. Qed.
Lemma sqrq_conj x : sqrq (x ^*q) = sqrq x.
Proof. by rewrite /sqrq normN. Qed.
Lemma conjqP x : x * x^*q = (sqrq x)%:q.
Proof.
rewrite /mulq /=; congr mkQuat.
by rewrite /= dotmulvN dotmulvv opprK -expr2.
by rewrite scalerN addNr add0r linearNr (@liexx _ (vec3 R)) oppr0.
Qed.
Lemma conjqZ k x : (k *: x) ^*q = k *: x ^*q.
Proof. by congr mkQuat; rewrite /= scalerN. Qed.
Lemma conjqN (u : 'rV[R]_3) : (- u%:v)^*q = - u%:v^*q.
Proof. by rewrite 2!conjq_def /= opprK oppr0 quat_vectN opprK. Qed.
Lemma pureq_conj x : (x \is pureq) = (x + x^*q == 0).
Proof.
case: x => x1 x2; rewrite qualifE /=; apply/idP/idP=> [/eqP->{x1}|].
by rewrite conjq_def /= quat_vectN subrr.
by rewrite conjq_def /= => /eqP[/eqP]; rewrite -mulr2n (mulrn_eq0 x1 2).
Qed.
Lemma conjqE x :
x^*q = - (1 / 2%:R) *: (x + `i * x * `i + `j * x * `j + `k * x * `k).
Proof.
apply/eqP; rewrite eq_quat; apply/andP; split; apply/eqP.
rewrite [in LHS]/= scaleqE /=.
rewrite !(mul0r,mulr0,addr0) scale0r !add0r !dotmulDl.
rewrite dotmulZv dotmulvv normeE expr1n mulr1 dotmulC
dot_crossmulC (@liexx _ (vec3 R)) dotmul0v addr0.
rewrite subrr add0r dotmulZv dotmulvv normeE expr1n mulr1
dotmulC dot_crossmulC (@liexx _ (vec3 R)) .
rewrite dotmul0v addr0 dotmulZv dotmulvv normeE expr1n mulr1
opprD addrA dotmulC dot_crossmulC.
rewrite (@liexx _ (vec3 R)) dotmul0v subr0 -opprD mulrN mulNr
opprK -mulr2n -(mulr_natl x.1) mulrA.
by rewrite div1r mulVr ?mul1r // unitfE pnatr_eq0.
rewrite /= !(mul0r,scale0r,add0r,addr0).
rewrite [_ *v 'e_0](@lieC _ (vec3 R)) /= ['e_0 *v _]linearD /= ['e_0 *v _]linearZ /= (@liexx _ (vec3 R)) .
rewrite scaler0 add0r double_crossmul dotmulvv normeE expr1n scale1r.
rewrite [_ *v 'e_1](@lieC _ (vec3 R)) /= ['e_1 *v _]linearD /= ['e_1 *v _]linearZ /= (@liexx _ (vec3 R)) .
rewrite scaler0 add0r double_crossmul dotmulvv normeE expr1n scale1r.
rewrite [_ *v 'e_2%:R](@lieC _ (vec3 R)) /= ['e_2%:R *v _]linearD /=
['e_2%:R *v _]linearZ /= (@liexx _ (vec3 R)).
rewrite scaler0 add0r double_crossmul dotmulvv normeE expr1n scale1r.
rewrite [X in _ = - _ *: X](_ : _ = 2%:R *:x.2).
by rewrite scalerA mulNr div1r mulVr ?unitfE ?pnatr_eq0 // scaleN1r.
rewrite !opprB (addrCA _ x.2) addrA -mulr2n scaler_nat -[RHS]addr0 -3!addrA;
congr (_ + _).
do 3 rewrite (addrCA _ x.2).
do 2 rewrite addrC -!addrA.
rewrite -opprB (scaleNr _ 'e_0) opprK -mulr2n addrA -mulr2n.
rewrite addrC addrA -opprB scaleNr opprK -mulr2n.
rewrite opprD.
rewrite (addrCA (- _ *: 'e_2%:R)).
rewrite -opprB scaleNr opprK -mulr2n.
rewrite -!mulNrn.
rewrite addrA.
rewrite -opprD.
rewrite -mulr2n.
rewrite -mulNrn.
rewrite -3!mulrnDl -scaler_nat.
apply/eqP; rewrite scalemx_eq0 pnatr_eq0 /=.
rewrite addrA addrC eq_sym -subr_eq add0r opprB opprD 2!opprK.
rewrite !['e__ *d _]dotmulC !dotmul_delta_mx /=.
rewrite addrA.
by rewrite -vec3E.
Qed.
Lemma conjq_scalar x : x.1%:q = (1 / 2%:R) *: (x + x^*q).
Proof.
case: x => x1 x2.
rewrite /conjq /= addqE /addq /= subrr quat_realD scalerDr -scalerDl.
by rewrite -splitr scale1r.
Qed.
Lemma conjq_vector x : x.2%:v = (1 / 2%:R) *: (x - x^*q).
Proof.
case: x => x1 x2.
rewrite /conjq /= addqE /addq /= subrr opprK.
rewrite quat_vectD scalerDr -scalerDl.
by rewrite -splitr scale1r.
Qed.
Definition invq a := (1 / sqrq a) *: (a ^*q).
Definition unitq : pred (quat R) := [pred a | a != 0%:q].
Lemma mulVq : {in unitq, left_inverse 1 invq (@mulq R)}.
Proof.
move=> a; rewrite inE /= => a0.
rewrite /invq -mulqE -quatAl conjq_comm conjqP.
by rewrite -quat_realZ mul1r mulVf // sqrq_eq0.
Qed.
Lemma mulqV : {in unitq, right_inverse 1 invq (@mulq R)}.
Proof.
move=> a; rewrite inE /= => a0.
by rewrite /invq -mulqE -quatAr conjqP -quat_realZ mul1r mulVf // sqrq_eq0.
Qed.
Lemma quat_integral x y : (x * y == 0) = ((x == 0) || (y == 0)).
Proof.
case: (x =P 0) => [->|/eqP xNZ] /=; first by rewrite mul0r eqxx.
apply/eqP/eqP => [xyZ|->]; last by rewrite mulr0.
by rewrite -[y]mul1r -(@mulVq x) // -mulrA xyZ mulr0.
Qed.
Lemma unitqP x y : y * x = 1 /\ x * y = 1 -> unitq x.
Proof.
move=> [ba1 ab1]; rewrite /unitq inE; apply/eqP => x0.
move/esym: ab1; rewrite x0 mul0r.
apply/eqP; exact: oneq_neq0.
Qed.
Lemma invq0id : {in [predC unitq], invq =1 id}.
Proof.
move=> a; rewrite !inE negbK => /eqP ->.
by rewrite /invq /= conjq0 scaler0.
Qed.
HB.instance Definition _ := @GRing.Ring_hasMulInverse.Build (quat R) _ _ mulVq mulqV unitqP invq0id.
Lemma invqE x : x^-1 = invq x. Proof. by done. Qed.
Definition normq x := Num.sqrt (sqrq x).
Lemma normq0 : normq 0 = 0.
Proof. by rewrite /normq /sqrq expr0n /= norm0 add0r expr0n sqrtr0. Qed.
Lemma normqc x : normq x^*q = normq x.
Proof. by rewrite /normq /sqrq /= normN. Qed.
Lemma normqE x : (normq x ^+ 2)%:q = x^*q * x.
Proof.
rewrite -normqc /normq sqr_sqrtr; last by rewrite /sqrq addr_ge0 // sqr_ge0.
by rewrite -conjqP conjqI.
Qed.
Lemma normq_ge0 x : 0 <= normq x.
Proof. by apply sqrtr_ge0. Qed.
Lemma normq_eq0 x : (normq x == 0) = (x == 0).
Proof. by rewrite /normq -{1}sqrtr0 eqr_sqrt ?sqrq_ge0// sqrq_eq0. Qed.
Lemma normq_vector (u : 'rV[R]_3) : normq u%:v = norm u.
Proof.
by rewrite /normq /sqrq /= expr0n add0r sqrtr_sqr ger0_norm ?norm_ge0.
Qed.
Lemma normqM x y : normq (x * y) = normq x * normq y.
Proof.
apply/eqP; rewrite -(@eqr_expn2 _ 2) // ?normq_ge0 //; last first.
by rewrite mulr_ge0 // normq_ge0.
rewrite -quat_scalarE normqE conjqM -mulrA (mulrA x^*q) -normqE.
rewrite quat_algE mulr_algl -scalerAr exprMn quat_realM.
by rewrite (normqE y) -mulr_algl quat_algE.
Qed.
Lemma normqZ (k : R) x : normq (k *: x) = `|k| * normq x.
Proof.
by rewrite /normq /sqrq /= normZ 2!exprMn sqr_normr -mulrDr sqrtrM ?sqr_ge0 //
sqrtr_sqr.
Qed.
Lemma normqV x : normq (x^-1) = normq x / sqrq x.
Proof.
rewrite invqE /invq normqZ ger0_norm; last first.
by rewrite divr_ge0 // ?ler01 // /sqrq addr_ge0 // sqr_ge0.
by rewrite normqc mulrC mul1r.
Qed.
Definition normQ x := (normq x)%:q.
Lemma normQ_eq0 x : (normQ x == 0) = (x == 0).
Proof. by rewrite /normQ quat_scalarE normq_eq0. Qed.
Definition normalizeq x : quat R := 1 / normq x *: x.
Lemma normalizeq1 x : x != 0 -> normq (normalizeq x) = 1.
Proof.
move=> x0; rewrite /normalizeq normqZ normrM normr1 mul1r normrV; last first.
by rewrite unitfE normq_eq0.
by rewrite ger0_norm ?normq_ge0 // mulVr // unitfE normq_eq0.
Qed.
Definition lequat x y := (x.2 == y.2) && (x.1 <= y.1).
Lemma lequat_normD x y : lequat (normQ (x + y)) (normQ x + normQ y).
Proof.
rewrite /lequat /= add0r eqxx andTb /normq /sqrq !sqr_norm !sum3E /= !mxE.
pose X := nth 0 [:: x.1; x _i; x _j; x _k].
pose Y := nth 0 [:: y.1; y _i; y _j; y _k].
suff: Num.sqrt (\sum_(i < 4) (X i + Y i)^+2) <=
Num.sqrt (\sum_(i < 4) (X i) ^+ 2) + Num.sqrt (\sum_(i < 4) (Y i) ^+ 2).
by rewrite !sum4E /X /Y /= !addrA.
have sqr_normE (x1 : R) : `|x1| ^+2 = x1 ^+ 2.
by case: (ltrgt0P x1); rewrite ?sqrrN // => ->.
have ler_mul_norm (x1 y1 : R) : x1 * y1 <= `|x1| * `|y1|.
rewrite {1}(numEsign x1) {1}(numEsign y1) mulrAC mulrA -signr_addb.
rewrite -mulrA [_ * `|x1|]mulrC.
case: (_ (+) _); rewrite !(expr0, expr1, mulNr, mul1r) //.
rewrite -subr_gte0 opprK -mulr2n; apply: mulrn_wge0.
by apply: mulr_ge0; apply: normr_ge0.
apply: le_trans (_ : Num.sqrt (\sum_(i < 4) (`|X i| + `|Y i|) ^+ 2) <= _).
rewrite -ler_sqr ?nnegrE; try by apply: sqrtr_ge0.
rewrite !sqr_sqrtr; try by apply: sumr_ge0 => i _; apply: sqr_ge0.
apply: ler_sum => i _; rewrite !sqrrD.
by rewrite !sqr_normE; do ! apply: ler_add => //.
rewrite -ler_sqr ?nnegrE; last 2 first.
- by apply: sqrtr_ge0.
- by apply: addr_ge0; apply: sqrtr_ge0.
rewrite [in X in _ <= X]sqrrD !sqr_sqrtr;
try by apply: sumr_ge0 => i ; rewrite sqr_ge0.
under eq_bigr do rewrite sqrrD.
rewrite 2!big_split /= sumrMnl.
under [X in _ <= X + _ + _]eq_bigr do rewrite -sqr_normE.
under [X in _ <= _ + _ X * _ *+2 + _]eq_bigr do rewrite -sqr_normE.
under [X in _ <= _ + _ + X]eq_bigr do rewrite -sqr_normE.
under [X in _ <= _ + _ * _ X *+2 + _]eq_bigr do rewrite -sqr_normE.
do 2 (apply: ler_add => //); rewrite ler_muln2r /=.
rewrite -ler_sqr ?nnegrE; last 2 first.
- by apply: sumr_ge0 => i _; apply: mulr_ge0; apply: normr_ge0.
- by apply: mulr_ge0; apply: sqrtr_ge0.
rewrite exprMn !sqr_sqrtr; last 2 first.
- by apply: sumr_ge0=> i _; apply: sqr_ge0.
- by apply: sumr_ge0=> i _; apply: sqr_ge0.
(* This is Cauchy Schwartz *)
rewrite -[_ <= _]orFb -[false]/(2 == 0)%nat -ler_muln2r.
pose u := \sum_(i < 4) \sum_(j < 4) (`|X i| * `|Y j| - `|X j| * `|Y i|) ^+ 2.
set z1 := \sum_(i < _) _; set z2 := \sum_(i < _) _; set z3 := \sum_(i < _) _.
suff ->: z2 * z3 *+ 2 = z1 ^+ 2 *+ 2 + u.
rewrite -{1}(addr0 (_ *+ 2)).
apply: ler_add => //.
by apply: sumr_ge0 => i _; apply: sumr_ge0 => j _; apply: sqr_ge0.
under [X in _ = _ + X]eq_bigr do
(under eq_bigr do (rewrite sqrrB !exprMn); rewrite !(sumrN, big_split));
rewrite !(sumrN, big_split, addrA) /=.
under eq_bigr do rewrite -mulr_sumr; rewrite -mulr_suml -/z2 -/z3.
have mswap (a b c d : R) : a * b * (c * d) = (c * b) * (a * d).
by rewrite mulrC mulrAC [a * _]mulrC !mulrA.
under [X in _ = _ - (X + _) + _]eq_bigr do
(under eq_bigr do rewrite mswap; rewrite -mulr_suml);
rewrite -mulr_sumr -expr2 -/z1.
under [X in _ = _ - (_ + X) + _]eq_bigr do
(under eq_bigr do rewrite mswap; rewrite -mulr_suml);
rewrite -mulr_sumr -expr2 -/z1 -mulr2n.
under [X in _ = _ + X]eq_bigr do rewrite -mulr_suml;
rewrite -mulr_sumr -/z2 -/z3.
by rewrite [_ *+ 2 + _]addrC addrK mulr2n.
Qed.
Definition ltquat x y := (x.2 == y.2) && (x.1 < y.1).
Lemma ltquat0_add x y : ltquat 0 x -> ltquat 0 y -> ltquat 0 (x + y).
Proof.
case: x => x0 x1; case: y => y0 y1; rewrite /ltquat /=.
move=> /andP[/eqP<- x0P] /andP[/eqP<- u0P] /=.
by rewrite addr0 eqxx addr_gt0.
Qed.
Lemma ge0_lequat_total x y :
lequat 0 x -> lequat 0 y -> lequat x y || lequat y x.
Proof.
case: x => x0 x1; case: y => y0 y1; rewrite /lequat /=.
move=> /andP[/eqP<- x0P] /andP[/eqP<- y0P] /=.
case: (lerP x0 y0); rewrite eqxx //=.
by apply: ltW.
Qed.
Lemma normQM x y : normQ (x * y) = normQ x * normQ y.
Proof. by rewrite {1}/normQ normqM quat_realM. Qed.
Lemma lequat_def x y : lequat x y = (normQ (y - x) == y - x).
Proof.
case: x => x0 x1; case: y => y0 y1; rewrite /normQ /normq /sqrq /=.
apply/idP/idP.
rewrite /lequat /=.
case/andP => /eqP<- x0Ly0.
apply/eqP; congr mkQuat; rewrite ?subrr ?expr0n ?addr0 //=.
rewrite norm0 expr0n addr0 sqrtr_sqr.
by apply/eqP; rewrite eqr_norm_id subr_ge0.
case/eqP => /eqP H H1.
move: (sym_equal H1) H => /subr0_eq->.
rewrite /lequat /= eqxx /=.
by rewrite subrr norm0 expr0n addr0 sqrtr_sqr eqr_norm_id subr_ge0.
Qed.
Lemma ltquat_def x y : ltquat x y = (y != x) && lequat x y.
Proof.
case: x => x0 x1; case: y => y0 y1 /=.
apply/andP/and3P => [[/eqP<- x0Ly0] | ].
split=> //.
by apply/negP; case/eqP => y0E; rewrite y0E // ltxx in x0Ly0.
by apply: ltW.
rewrite eq_quat negb_and /= => [] [/orP[y0Dx0 | y1Dx1] x1Ey1 x0Ly0];
split => //.
by rewrite lt_neqAle eq_sym y0Dx0.
by rewrite eq_sym x1Ey1 in y1Dx1.
Qed.
Fail Definition quat_POrderedMixin :=
NumMixin lequat_normD ltquat0_add eq0_normQ ge0_lequat_total
normQM lequat_def ltquat_def.
Fail Canonical Structure quat_numDomainType :=
NumDomainType _ quat_POrderedMixin.
Definition uquat := [qualify x : quat R | normq x == 1].
Fact uquat_key : pred_key uquat. Proof. by []. Qed.
Canonical uquat_keyed := KeyedQualifier uquat_key.
Lemma uquatE x : (x \is uquat) = (sqrq x == 1).
Proof. by rewrite qualifE /normq -{1}sqrtr1 eqr_sqrt // ?sqrq_ge0// ler01. Qed.
Lemma muluq_proof x y : x \is uquat -> y \is uquat -> x * y \is uquat.
Proof. by rewrite 3!qualifE => /eqP Hq /eqP Hp; rewrite normqM Hq Hp mulr1. Qed.
Lemma invq_uquat x : x \is uquat -> x^-1 = x^*q.
Proof.
by rewrite uquatE => /eqP Hq; rewrite invqE /invq Hq invr1 mul1r scale1r.
Qed.
Lemma invuq_proof x : x \is uquat -> normq (x^-1) == 1.
Proof. by move=> ux; rewrite invq_uquat // normqc. Qed.
Lemma cos_atan_uquat x : x \is uquat -> x \isn't pureq ->
let a := atan (norm x.2 / x.1) in cos a ^+ 2 = x.1 ^+ 2.
Proof.
move=> ux q00 a.
rewrite cos_atan exprMn [x.1 ^-1 ^+2]exprVn.
have /divff <- : x.1 ^+ 2 !=0 by rewrite sqrf_eq0.
rewrite -mulrDl.
rewrite uquatE /sqrq in ux; rewrite (eqP ux) mul1r.
by rewrite -exprVn sqrtr_sqr normfV invrK sqr_normr.
Qed.
Lemma sin_atan_uquat x : x \is uquat -> x \isn't pureq ->
let a := atan (norm x.2 / x.1) in sin a ^+ 2 = norm x.2 ^+ 2.
Proof.
move=> ux q00 a.
rewrite /a sqr_sin_atan.
have /divrr <- : x.1 ^+ 2 \in GRing.unit by rewrite unitfE sqrf_eq0.
rewrite uquatE /sqrq in ux.
rewrite expr_div_n -mulrDl.
by rewrite (eqP ux) mul1r invrK -mulrA mulVr ?mulr1 // unitrX // unitfE.
Qed.
End quaternion1.
Arguments uquat {R}.
Section conjugation.
Variable R : realType.
Implicit Types (x : quat R) (u : 'rV[R]_3).
Definition conjugation x u : quat R := x * u%:v * x^*q.
Lemma conjugation_is_pure x u : conjugation x u \is pureq.
Proof.
rewrite pureq_conj /conjugation conjqM conjqI conjqM mulrA -mulrDl -mulrDr.
by have := pureq_conj u%:v; rewrite qualifE /= eqxx => /esym/eqP ->; Simp.r.
Qed.
Lemma conjugationE x u : conjugation x u =
((x.1 ^+ 2 - norm x.2 ^+ 2) *: u +
((x.2 *d u) *: x.2) *+ 2 +
(x.1 *: (x.2 *v u)) *+ 2)%:v.
Proof.
case: x => x1 x2 /=; rewrite /conjugation /= /conjq /= mulqE /mulq /=.
rewrite mulr0 scale0r addr0 add0r; congr mkQuat.
rewrite dotmulvN opprK dotmulDl (dotmulC (_ *v _) x2) dot_crossmulC.
by rewrite (@liexx _ (vec3 R)) dotmul0v addr0 dotmulZv mulNr mulrC dotmulC addrC subrr.
rewrite scalerDr scalerA -expr2 addrCA scalerBl -!addrA; congr (_ + _).
rewrite [in X in _ + X = _]linearN /= (@lieC _ (vec3 R) _ x2)/= linearD /= opprK.
rewrite linearZ /= (addrA (x1 *: _ )) -mulr2n.
rewrite [in LHS]addrCA 2![in RHS]addrA [in RHS]addrC; congr (_ + _).
rewrite scalerN scaleNr opprK -addrA addrCA; congr (_ + _).
by rewrite double_crossmul [in RHS]addrC dotmulvv.
Qed.
Lemma conjugation_uquat x : x \is uquat -> conjugation x x.2 = (x.2)%:v.
Proof.
rewrite uquatE /sqrq => /eqP xu.
rewrite conjugationE (@liexx _ (vec3 R)) scaler0 mul0rn addr0 dotmulvv scalerBl mulr2n addrA.
by rewrite subrK -scalerDl xu scale1r.
Qed.
Lemma conjugation_axis x k : x \is uquat ->
conjugation x (k *: x.2) = (k *: x.2)%:v.
Proof.
move=> xu; rewrite /conjugation quat_vectZ -scalerAr -scalerAl.
by rewrite -/(conjugation x x.2) conjugation_uquat.
Qed.
Lemma norm_conjugation x u : x \is uquat -> normq (conjugation x u) = norm u.
Proof.
rewrite qualifE => /eqP x1; rewrite /conjugation 2!normqM normqc x1; Simp.r.
by rewrite normq_vector.
Qed.
End conjugation.
Section polar_coordinates.
Variable R : realType.
Implicit Types (x : quat R) (v : 'rV[R]_3) (a : R).
Definition quat_of_polar a v := mkQuat (cos a) (sin a *: v).
Lemma quat_of_polar01 : quat_of_polar 0 'e_1 = 1%:q.
Proof. by rewrite /quat_of_polar /= cos0 sin0 scale0r. Qed.
Lemma quat_of_polarpi1 : quat_of_polar pi 'e_1 = (-1)%:q.
Proof. by rewrite /quat_of_polar cospi sinpi scale0r. Qed.
Lemma quat_of_polarpihalf v : quat_of_polar (pi / 2%:R) v = v%:v.
Proof. by rewrite /quat_of_polar cos_pihalf sin_pihalf scale1r. Qed.
Lemma uquat_of_polar a v (v1 : norm v = 1) : quat_of_polar a v \is uquat.
Proof.
by rewrite uquatE /quat_of_polar /sqrq /= normZ v1 mulr1 sqr_normr cos2Dsin2.
Qed.
Definition quat_rot x v : 'rV[R]_3 := (conjugation x v).2.
Lemma conjugation_quat_of_polar_axis v a : norm v = 1 ->
quat_rot (quat_of_polar a v) v = v.
Proof.
move=> v1.
rewrite /quat_rot conjugationE /= normZ exprMn v1 expr1n mulr1 sqr_normr.
rewrite dotmulZv dotmulvv v1 expr1n mulr1 linearZl_LR (@liexx _ (vec3 R)) /= 2!scaler0 mul0rn.
rewrite addr0 scalerA -expr2 mulr2n scalerBl addrA subrK -scalerDl cos2Dsin2.
by rewrite scale1r.
Qed.
Local Open Scope frame_scope.
Lemma conjugation_quat_of_polar_frame_j (f : frame R) a :
quat_rot (quat_of_polar a f~i) f~j =
cos (a *+ 2) *: f~j + sin (a *+ 2) *: f~k.
Proof.
rewrite /quat_rot conjugationE /= normZ noframe_norm mulr1 sqr_normr dotmulZv.
have v0 : f~i != 0 by rewrite -norm_eq0 noframe_norm oner_neq0.
rewrite (noframe_idotj f) mulr0 scale0r mul0rn addr0 linearZl_LR /=.
rewrite (frame_icrossj f) scalerA [in RHS]mulr2n cosD sinD -!expr2.
by congr (_ + _); rewrite (mulrC (sin a)) -mulr2n -scalerMnl.
Qed.
Lemma conjugation_quat_of_polar_frame_k (f : frame R) a :
quat_rot (quat_of_polar a f~i) f~k =
- sin (a *+ 2) *: f~j + cos (a *+ 2) *: f~k.
Proof.
rewrite /quat_rot conjugationE /= normZ noframe_norm mulr1 sqr_normr dotmulZv.
have v0 : f~i != 0 by rewrite -norm_eq0 noframe_norm oner_neq0.
rewrite (noframe_idotk f) mulr0 scale0r mul0rn addr0 linearZl_LR /=.
rewrite (frame_icrossk f) 2!scalerN scalerA sinD cosD -!expr2 addrC scaleNr.
by congr (_ + _); rewrite (mulrC (sin a)) -mulr2n -scalerMnl mulNrn.
Qed.
Definition polar_of_quat x : (R * 'rV_3)%type :=
if x.2 == 0 then
if x.1 == 1 then (0, 'e_1) else (pi, 'e_1)
else if x.1 == 0 then (pi / 2%:R, x.2) else
let: u := normalize x.2 in
let: a := atan (norm x.2 / x.1) in
if 0 < x.1 then (a, u) else (a + pi, u).
Lemma polar_of_quat0 : polar_of_quat 0 = (pi, 'e_1).
Proof. by rewrite /polar_of_quat eqxx eq_sym oner_eq0. Qed.
Lemma norm_polar_of_quat x : x \is uquat -> norm (polar_of_quat x).2 = 1.
Proof.
case: x => a0 a1; rewrite /= qualifE /polar_of_quat /normq /sqrq /=.
have [/eqP ->|a10] := ifPn; first by case: ifPn; rewrite norm_delta_mx.
case: (sgzP a0) => [-> /eqP| |]; try by rewrite norm_normalize.
by rewrite expr0n add0r sqrtr_sqr ger0_norm // norm_ge0.
Qed.
Lemma polar_of_quatK x : x \is uquat ->
quat_of_polar (polar_of_quat x).1 (polar_of_quat x).2 = x.
Proof.
case: x => a0 a1; rewrite /= qualifE /polar_of_quat /normq /sqrq /=.
have [->|/eqP a1N u1] := a1 =P 0.
rewrite norm0 expr0n addr0 sqrtr_sqr; have [?/eqP->|?|_] := ltrgt0P a0.
- by rewrite eqxx quat_of_polar01.
- by rewrite eqr_oppLR => /eqP ->; rewrite eqrNxx oner_eq0 quat_of_polarpi1.
- by rewrite eq_sym oner_eq0.
move: u1; have [-> _|a0P /eqP u1 |a0N /eqP u1] := sgzP a0.
- by rewrite quat_of_polarpihalf.
- congr mkQuat.
by rewrite cos_atan sqrtr_1sqr2 ?gt_eqF// gtr0_norm// invrK.
rewrite sin_atan sqrtr_1sqr2 ?gt_eqF// gtr0_norm// invrK -mulrA.
by rewrite mulVf ?gt_eqF// mulr1 norm_scale_normalize.
- congr mkQuat.
rewrite cosDpi cos_atan sqrtr_1sqr2 ?lt_eqF// invrK ltr0_norm//.
by rewrite opprK.
rewrite sinDpi sin_atan sqrtr_1sqr2// ?lt_eqF// ltr0_norm// 2!invrN mulrN.
by rewrite invrK opprK -mulrA mulVf ?lt_eqF// mulr1 norm_scale_normalize.
Qed.
Lemma quat_rot_is_linear x : linear (quat_rot x).
Proof.
move=> k u v; rewrite /quat_rot !conjugationE.
rewrite scalerDr scalerA (mulrC _ k) -scalerA.
rewrite 2![in RHS]scalerDr -2![in LHS]addrA -3![in RHS]addrA; congr (_ + _).
rewrite [in RHS]addrA [in RHS]addrCA -[in RHS]addrA; congr (_ + _).
rewrite dotmulDr scalerDl mulrnDl -addrA addrCA; congr (_ + _).
rewrite dotmulvZ -scalerA scalerMnr -addrA; congr (_ + _).
rewrite linearD /= scalerDr mulrnDl; congr (_ + _).
by rewrite linearZ /= scalerA mulrC -scalerA -scalerMnr.
Qed.
HB.instance Definition _ x := @GRing.isLinear.Build _ _ _ _ _ (quat_rot_is_linear x).
Lemma quat_rot_isRot_polar v a : norm v = 1 ->
isRot (a *+2) v [linear of quat_rot (quat_of_polar a v)].
Proof.