Continuous linear maps on products and Pi types #
In this file, we collect various constructions relating continuous linear maps with (binary or arbitrary) products.
Main definitions #
Binary products (viewed as categorical products):
ContinuousLinearMap.fst R M₁ M₂ : M₁ × M₂ →L[R] M₁andContinuousLinearMap.snd R M₁ M₂ : M₁ × M₂ →L[R] M₂are the two projections, given respectively byfst (x, y) = xandsnd (x, y) = y. These are the continuous versions ofLinearMap.fstandLinearMap.snd.ContinuousLinearMap.prod f₁ f₂is the continuous linear mapM →L[R] N₁ × N₂given by two continuous linear mapsf₁ : M →L[R] N₁andf₂ : M →L[R] N₂. This is the continuous version ofLinearMap.prod.ContinuousLinearMap.prodEquivshows that the above is a bijection: every continuous linear map to a product is obtained this way. In other words, this is the universal property of the product.ContinuousLinearMap.prodMap f₁ f₂is the continuous linear mapM₁ × M₂ →L[R] N₁ × N₂given by two continuous linear mapsf₁ : M₁ →L[R] N₁andf₂ : M₂ →L[R] N₂. This is the continuous version ofLinearMap.prodMap.
Binary products (viewed as categorical coproducts):
ContinuousLinearMap.inl R M₁ M₂ : M₁ →L[R] M₁ × M₂andContinuousLinearMap.inr R M₁ M₂ : M₂ →L[R] M₁ × M₂are the two inclusions, given respectively byinl x = (x, 0)andinr x = (0, x). These are the continuous versions ofLinearMap.inlandLinearMap.inr.ContinuousLinearMap.coprod f₁ f₂is the continuous linear mapM₁ × M₂ →L[R] Ngiven by two continuous linear mapsf₁ : M₁ →L[R] Nandf₂ : M₂ →L[R] N. This is the continuous version ofLinearMap.coprod.ContinuousLinearMap.coprodEquivshows that the above is a bijection: every continuous linear map from a (binary) product is obtained this way. In other words, this is the universal property of the coproduct.
Indexed products:
ContinuousLinearMap.pi fis the continuous linear mapM →L[R] (Π i, N i)given by a familyf₁ : Π i, M →L[R] N iof continuous linear maps. This is the continuous version ofLinearMap.pi.ContinuousLinearMap.piMap fis the continuous linear map(Π i, M i) →L[R] (Π i, N i)given by a familyf : Π i, M i →L[R] N iof continuous linear maps. This is the continuous version ofLinearMap.piMap.ContinuousLinearMap.proj j : (Π i, M i) →L[R] M jis the projection given byproj i f = f i. This is the continuous version ofLinearMap.proj.
Properties that hold for non-necessarily commutative semirings. #
The Cartesian product of two bounded linear maps, as a bounded linear map.
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The left injection into a product is a continuous linear map.
Equations
- ContinuousLinearMap.inl R M₁ M₂ = (ContinuousLinearMap.id R M₁).prod 0
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The right injection into a product is a continuous linear map.
Equations
- ContinuousLinearMap.inr R M₁ M₂ = ContinuousLinearMap.prod 0 (ContinuousLinearMap.id R M₂)
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Prod.fst as a ContinuousLinearMap.
Equations
- ContinuousLinearMap.fst R M₁ M₂ = { toLinearMap := LinearMap.fst R M₁ M₂, cont := ⋯ }
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Prod.snd as a ContinuousLinearMap.
Equations
- ContinuousLinearMap.snd R M₁ M₂ = { toLinearMap := LinearMap.snd R M₁ M₂, cont := ⋯ }
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Prod.map of two continuous linear maps.
Equations
- f₁.prodMap f₂ = (f₁ ∘SL ContinuousLinearMap.fst R M₁ M₃).prod (f₂ ∘SL ContinuousLinearMap.snd R M₁ M₃)
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pi construction for continuous linear functions. From a family of continuous linear functions
it produces a continuous linear function into a family of topological modules.
Equations
- ContinuousLinearMap.pi f = { toLinearMap := LinearMap.pi fun (i : ι) => ↑(f i), cont := ⋯ }
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The projections from a family of topological modules are continuous linear maps.
Equations
- ContinuousLinearMap.proj i = { toLinearMap := LinearMap.proj i, cont := ⋯ }
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Construct a continuous linear map between two (dependent) function spaces
by applying index-dependent linear maps to the coordinates.
A bundled version of Pi.map.
If the index type is finite, then this map can be seen as a “block diagonal” map between indexed products of modules.
Equations
- ContinuousLinearMap.piMap f = ContinuousLinearMap.pi fun (i : ι) => f i ∘SL ContinuousLinearMap.proj i
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Given a function f : α → ι, it induces a continuous linear function by right composition on
product types. For f = Subtype.val, this corresponds to forgetting some set of variables.
Equations
- Pi.compRightL R φ f = { toFun := fun (v : (i : ι) → φ i) (i : α) => v (f i), map_add' := ⋯, map_smul' := ⋯, cont := ⋯ }
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Pi.single as a bundled continuous linear map.
Equations
- ContinuousLinearMap.single R φ i = { toLinearMap := LinearMap.single R φ i, cont := ⋯ }
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ContinuousLinearMap.prod as an Equiv.
Equations
- One or more equations did not get rendered due to their size.
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ContinuousLinearMap.prod as a LinearEquiv.
See ContinuousLinearMap.prodL for the ContinuousLinearEquiv version.
Equations
- ContinuousLinearMap.prodₗ S = { toFun := ContinuousLinearMap.prodEquiv.toFun, map_add' := ⋯, map_smul' := ⋯, invFun := ContinuousLinearMap.prodEquiv.invFun, left_inv := ⋯, right_inv := ⋯ }
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The continuous linear map given by (x, y) ↦ f₁ x + f₂ y.
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Taking the product of two maps with the same codomain is equivalent to taking the product of
their domains.
See note [bundled maps over different rings] for why separate R and S semirings are used.
See ContinuousLinearMap.coprodEquivL for the ContinuousLinearEquiv version.
Equations
- One or more equations did not get rendered due to their size.