Quadratic form structures related to Module.Dual

Main definitions

• LinearMap.dualProd R M, the bilinear form on (f, x) : Module.Dual R M × M defined as f x.
• QuadraticForm.dualProd R M, the quadratic form on (f, x) : Module.Dual R M × M defined as f x.
• QuadraticForm.toDualProd : (Q.prod <| -Q) →qᵢ QuadraticForm.dualProd R M a form-preserving map from (Q.prod <| -Q) to QuadraticForm.dualProd R M.

@[simp]

theorem LinearMap.dualProd_apply_apply (R : Type u_1) (M : Type u_2) [CommSemiring R] [AddCommMonoid M] [Module R M] (a : Module.Dual R M × M) (a : Module.Dual R M × M) : ((LinearMap.dualProd R M) a✝) a = a.1 a✝.2 + a✝.1 a.2

def LinearMap.dualProd (R : Type u_1) (M : Type u_2) [CommSemiring R] [AddCommMonoid M] [Module R M] : LinearMap.BilinForm R (Module.Dual R M × M)

The symmetric bilinear form on Module.Dual R M × M defined as B (f, x) (g, y) = f y + g x.

Equations

• One or more equations did not get rendered due to their size.

theorem LinearMap.isSymm_dualProd (R : Type u_1) (M : Type u_2) [CommSemiring R] [AddCommMonoid M] [Module R M] : LinearMap.IsSymm (LinearMap.dualProd R M)

theorem LinearMap.separatingLeft_dualProd (R : Type u_1) (M : Type u_2) [CommRing R] [AddCommGroup M] [Module R M] : LinearMap.SeparatingLeft (LinearMap.dualProd R M) ↔ Function.Injective ⇑(Module.Dual.eval R M)

@[simp]

theorem QuadraticForm.dualProd_apply (R : Type u_1) (M : Type u_2) [CommSemiring R] [AddCommMonoid M] [Module R M] (p : Module.Dual R M × M) : (QuadraticForm.dualProd R M) p = p.1 p.2

def QuadraticForm.dualProd (R : Type u_1) (M : Type u_2) [CommSemiring R] [AddCommMonoid M] [Module R M] : QuadraticForm R (Module.Dual R M × M)

The quadratic form on Module.Dual R M × M defined as Q (f, x) = f x.

Equations

• QuadraticForm.dualProd R M = { toFun := fun (p : Module.Dual R M × M) => p.1 p.2, toFun_smul := ⋯, exists_companion' := ⋯ }

@[simp]

theorem LinearMap.dualProd.toQuadraticForm (R : Type u_1) (M : Type u_2) [CommSemiring R] [AddCommMonoid M] [Module R M] : LinearMap.BilinForm.toQuadraticForm (LinearMap.dualProd R M) = 2 • QuadraticForm.dualProd R M

@[simp]

theorem QuadraticForm.dualProdIsometry_toFun {R : Type u_1} {M : Type u_2} {N : Type u_3} [CommSemiring R] [AddCommMonoid M] [AddCommMonoid N] [Module R M] [Module R N] (f : M ≃ₗ[R] N) : ∀ (a : Module.Dual R M × M), (QuadraticForm.dualProdIsometry f) a = (AddEquiv.prodCongr ↑(LinearEquiv.dualMap (LinearEquiv.symm f)) ↑f) a

@[simp]

theorem QuadraticForm.dualProdIsometry_invFun {R : Type u_1} {M : Type u_2} {N : Type u_3} [CommSemiring R] [AddCommMonoid M] [AddCommMonoid N] [Module R M] [Module R N] (f : M ≃ₗ[R] N) : ∀ (a : Module.Dual R N × N), (QuadraticForm.dualProdIsometry f).invFun a = (AddEquiv.symm (AddEquiv.prodCongr ↑(LinearEquiv.dualMap (LinearEquiv.symm f)) ↑f)) a

def QuadraticForm.dualProdIsometry {R : Type u_1} {M : Type u_2} {N : Type u_3} [CommSemiring R] [AddCommMonoid M] [AddCommMonoid N] [Module R M] [Module R N] (f : M ≃ₗ[R] N) : QuadraticForm.IsometryEquiv (QuadraticForm.dualProd R M) (QuadraticForm.dualProd R N)

Any module isomorphism induces a quadratic isomorphism between the corresponding dual_prod.

Equations

• QuadraticForm.dualProdIsometry f = { toLinearEquiv := LinearEquiv.prod (LinearEquiv.symm (LinearEquiv.dualMap f)) f, map_app' := ⋯ }

@[simp]

theorem QuadraticForm.dualProdProdIsometry_toFun {R : Type u_1} {M : Type u_2} {N : Type u_3} [CommSemiring R] [AddCommMonoid M] [AddCommMonoid N] [Module R M] [Module R N] : ∀ (a : Module.Dual R (M × N) × M × N), QuadraticForm.dualProdProdIsometry a = ((LinearMap.comp a.1 (LinearMap.inl R M N), a.2.1), LinearMap.comp a.1 (LinearMap.inr R M N), a.2.2)

@[simp]

theorem QuadraticForm.dualProdProdIsometry_invFun {R : Type u_1} {M : Type u_2} {N : Type u_3} [CommSemiring R] [AddCommMonoid M] [AddCommMonoid N] [Module R M] [Module R N] : ∀ (a : (Module.Dual R M × M) × Module.Dual R N × N), QuadraticForm.dualProdProdIsometry.invFun a = (LinearEquiv.symm (LinearEquiv.prod (LinearEquiv.symm (Module.dualProdDualEquivDual R M N)) (LinearEquiv.refl R (M × N)))) ((a.1.1, a.2.1), a.1.2, a.2.2)

def QuadraticForm.dualProdProdIsometry {R : Type u_1} {M : Type u_2} {N : Type u_3} [CommSemiring R] [AddCommMonoid M] [AddCommMonoid N] [Module R M] [Module R N] : QuadraticForm.IsometryEquiv (QuadraticForm.dualProd R (M × N)) (QuadraticForm.prod (QuadraticForm.dualProd R M) (QuadraticForm.dualProd R N))

QuadraticForm.dualProd commutes (isometrically) with QuadraticForm.prod.

Equations

• One or more equations did not get rendered due to their size.

@[simp]

theorem QuadraticForm.toDualProd_apply {R : Type u_1} {M : Type u_2} [CommRing R] [AddCommGroup M] [Module R M] (Q : QuadraticForm R M) [Invertible 2] (i : M × M) : (QuadraticForm.toDualProd Q) i = ((QuadraticForm.associated Q) i.1 + (QuadraticForm.associated Q) i.2, i.1 - i.2)

def QuadraticForm.toDualProd {R : Type u_1} {M : Type u_2} [CommRing R] [AddCommGroup M] [Module R M] (Q : QuadraticForm R M) [Invertible 2] : QuadraticForm.prod Q (-Q) →qᵢ QuadraticForm.dualProd R M

The isometry sending (Q.prod <| -Q) to (QuadraticForm.dualProd R M).

This is σ from Proposition 4.8, page 84 of [Hermitian K-Theory and Geometric Applications][hyman1973]; though we swap the order of the pairs.

Equations

• One or more equations did not get rendered due to their size.

TODO: show that QuadraticForm.toDualProd is an QuadraticForm.IsometryEquiv