(Semi)linear equivalences #
In this file we define
LinearEquiv σ M M₂,M ≃ₛₗ[σ] M₂: an invertible semilinear map. Here,σis aRingHomfromRtoR₂and ane : M ≃ₛₗ[σ] M₂satisfiese (c • x) = (σ c) • (e x). The plain linear version, withσbeingRingHom.id R, is denoted byM ≃ₗ[R] M₂, and the star-linear version (withσbeingstarRingEnd) is denoted byM ≃ₗ⋆[R] M₂.
Implementation notes #
To ensure that composition works smoothly for semilinear equivalences, we use the typeclasses
RingHomCompTriple, RingHomInvPair and RingHomSurjective from
Algebra/Ring/CompTypeclasses.
The group structure on automorphisms, LinearEquiv.automorphismGroup, is provided elsewhere.
TODO #
- Parts of this file have not yet been generalized to semilinear maps
Tags #
linear equiv, linear equivalences, linear isomorphism, linear isomorphic
A linear equivalence is an invertible linear map.
- toFun : M → M₂
- invFun : M₂ → M
The backwards directed function underlying a linear equivalence.
- left_inv : Function.LeftInverse self.invFun self.toFun
LinearEquiv.invFunis a left inverse to the linear equivalence's underlying function. - right_inv : Function.RightInverse self.invFun self.toFun
LinearEquiv.invFunis a right inverse to the linear equivalence's underlying function.
Instances For
The additive equivalence of types underlying a linear equivalence.
Equations
- LinearEquiv.toAddEquiv self = { toEquiv := { toFun := self.toFun, invFun := self.invFun, left_inv := ⋯, right_inv := ⋯ }, map_add' := ⋯ }
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The notation M ≃ₛₗ[σ] M₂ denotes the type of linear equivalences between M and M₂ over a
ring homomorphism σ.
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The notation M ≃ₗ [R] M₂ denotes the type of linear equivalences between M and M₂ over
a plain linear map M →ₗ M₂.
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The notation M ≃ₗ⋆[R] M₂ denotes the type of star-linear equivalences between M and M₂
over the ⋆ endomorphism of the underlying starred ring R.
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SemilinearEquivClass F σ M M₂ asserts F is a type of bundled σ-semilinear equivs
M → M₂.
See also LinearEquivClass F R M M₂ for the case where σ is the identity map on R.
A map f between an R-module and an S-module over a ring homomorphism σ : R →+* S
is semilinear if it satisfies the two properties f (x + y) = f x + f y and
f (c • x) = (σ c) • f x.
Applying a semilinear equivalence
foverσtor • xequalsσ r • f x.
Instances
LinearEquivClass F R M M₂ asserts F is a type of bundled R-linear equivs M → M₂.
This is an abbreviation for SemilinearEquivClass F (RingHom.id R) M M₂.
Equations
- LinearEquivClass F R M M₂ = SemilinearEquivClass F (RingHom.id R) M M₂
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Equations
- ⋯ = ⋯
Equations
- LinearEquiv.instCoeLinearEquivLinearMap = { coe := LinearEquiv.toLinearMap }
The equivalence of types underlying a linear equivalence.
Equations
- LinearEquiv.toEquiv f = (LinearEquiv.toAddEquiv f).toEquiv
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Helper instance for when inference gets stuck on following the normal chain
EquivLike → FunLike.
TODO: this instance doesn't appear to be necessary: remove it (after benchmarking?)
Equations
- LinearEquiv.instFunLikeLinearEquiv = { coe := DFunLike.coe, coe_injective' := ⋯ }
Equations
- ⋯ = ⋯
The identity map is a linear equivalence.
Equations
- LinearEquiv.refl R M = let __src := LinearMap.id; let __src_1 := Equiv.refl M; { toLinearMap := __src, invFun := __src_1.invFun, left_inv := ⋯, right_inv := ⋯ }
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Linear equivalences are symmetric.
Equations
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See Note [custom simps projection]
Equations
- LinearEquiv.Simps.apply e = ⇑e
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See Note [custom simps projection]
Equations
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Linear equivalences are transitive.
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The notation e₁ ≪≫ₗ e₂ denotes the composition of the linear equivalences e₁ and e₂.
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Pretty printer defined by notation3 command.
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The two paths coercion can take to an AddMonoidHom are equivalent
Interpret a RingEquiv f as an f-semilinear equiv.
Equations
- RingEquiv.toSemilinearEquiv f = { toLinearMap := { toAddHom := { toFun := ⇑f, map_add' := ⋯ }, map_smul' := ⋯ }, invFun := f.invFun, left_inv := ⋯, right_inv := ⋯ }
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An involutive linear map is a linear equivalence.
Equations
- LinearEquiv.ofInvolutive f hf = let __src := Function.Involutive.toPerm (⇑f) hf; { toLinearMap := f, invFun := __src.invFun, left_inv := ⋯, right_inv := ⋯ }
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If M and M₂ are both R-semimodules and S-semimodules and R-semimodule structures
are defined by an action of R on S (formally, we have two scalar towers), then any S-linear
equivalence from M to M₂ is also an R-linear equivalence.
See also LinearMap.restrictScalars.
Equations
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Restriction from R-linear automorphisms of M to R-linear endomorphisms of M,
promoted to a monoid hom.
Equations
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The tautological action by M ≃ₗ[R] M on M.
This generalizes Function.End.applyMulAction.
Equations
- LinearEquiv.applyDistribMulAction = DistribMulAction.mk ⋯ ⋯
LinearEquiv.applyDistribMulAction is faithful.
Equations
- ⋯ = ⋯
Equations
- ⋯ = ⋯
Equations
- ⋯ = ⋯
Any two modules that are subsingletons are isomorphic.
Equations
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g : R ≃+* S is R-linear when the module structure on S is Module.compHom S g .
Equations
- Module.compHom.toLinearEquiv g = { toLinearMap := { toAddHom := { toFun := ⇑g, map_add' := ⋯ }, map_smul' := ⋯ }, invFun := ⇑(RingEquiv.symm g), left_inv := ⋯, right_inv := ⋯ }
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Each element of the group defines a linear equivalence.
This is a stronger version of DistribMulAction.toAddEquiv.
Equations
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Each element of the group defines a module automorphism.
This is a stronger version of DistribMulAction.toAddAut.
Equations
- DistribMulAction.toModuleAut R M = { toOneHom := { toFun := DistribMulAction.toLinearEquiv R M, map_one' := ⋯ }, map_mul' := ⋯ }
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An additive equivalence whose underlying function preserves smul is a linear equivalence.
Equations
- AddEquiv.toLinearEquiv e h = { toLinearMap := { toAddHom := { toFun := e.toFun, map_add' := ⋯ }, map_smul' := h }, invFun := e.invFun, left_inv := ⋯, right_inv := ⋯ }
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An additive equivalence between commutative additive monoids is a linear equivalence between ℕ-modules
Equations
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An additive equivalence between commutative additive groups is a linear equivalence between ℤ-modules
Equations
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The equivalence between R-linear maps from R to M, and points of M itself.
This says that the forgetful functor from R-modules to types is representable, by R.
This is an S-linear equivalence, under the assumption that S acts on M commuting with R.
When R is commutative, we can take this to be the usual action with S = R.
Otherwise, S = ℕ shows that the equivalence is additive.
See note [bundled maps over different rings].
Equations
- One or more equations did not get rendered due to their size.