Compactly supported continuous functions #
In this file, we define the type C_c(α, β) of compactly supported continuous functions and the
class CompactlySupportedContinuousMapClass, and prove basic properties.
Main definitions and results #
This file contains various instances such as Add, Mul, SMul F C_c(α, β) when F is a class of
continuous functions.
When β has more structures, C_c(α, β) inherits such structures as AddCommGroup,
NonUnitalRing and StarRing.
When the domain α is compact, ContinuousMap.liftCompactlySupported gives the identification
C(α, β) ≃ C_c(α, β).
C_c(α, β) is the type of continuous functions α → β with compact support from a topological
space to a topological space with a zero element.
When possible, instead of parametrizing results over f : C_c(α, β),
you should parametrize over {F : Type*} [CompactlySupportedContinuousMapClass F α β] (f : F).
When you extend this structure, make sure to extend CompactlySupportedContinuousMapClass.
- toFun : α → β
- continuous_toFun : Continuous self.toFun
- hasCompactSupport' : HasCompactSupport self.toFun
The function has compact support .
Instances For
C_c(α, β) is the type of continuous functions α → β with compact support from a topological
space to a topological space with a zero element.
When possible, instead of parametrizing results over f : C_c(α, β),
you should parametrize over {F : Type*} [CompactlySupportedContinuousMapClass F α β] (f : F).
When you extend this structure, make sure to extend CompactlySupportedContinuousMapClass.
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C_c(α, β) is the type of continuous functions α → β with compact support from a topological
space to a topological space with a zero element.
When possible, instead of parametrizing results over f : C_c(α, β),
you should parametrize over {F : Type*} [CompactlySupportedContinuousMapClass F α β] (f : F).
When you extend this structure, make sure to extend CompactlySupportedContinuousMapClass.
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CompactlySupportedContinuousMapClass F α β states that F is a type of continuous maps with
compact support.
You should also extend this typeclass when you extend CompactlySupportedContinuousMap.
- hasCompactSupport (f : F) : HasCompactSupport ⇑f
Each member of the class has compact support.
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Copy of a CompactlySupportedContinuousMap with a new toFun equal to the old one. Useful
to fix definitional equalities.
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A continuous function on a compact space automatically has compact support.
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Composition of a continuous function f with compact support with another continuous function
g sending 0 to 0 from the left yields another continuous function g ∘ f with compact
support.
If g doesn't send 0 to 0, f.compLeft g defaults to 0.
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Algebraic structure #
Whenever β has the structure of continuous additive monoid and a compatible topological structure,
then C_c(α, β) inherits a corresponding algebraic structure. The primary exception to this is that
C_c(α, β) will not have a multiplicative identity.
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the product of f : F assuming ContinuousMapClass F α γ and ContinuousSMul γ β and
g : C_c(α, β) is in C_c(α, β)
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Coercion to a function as a AddMonoidHom. Similar to AddMonoidHom.coeFn.
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Star structure #
It is possible to equip C_c(α, β) with a pointwise star operation whenever there is a continuous
star : β → β for which star (0 : β) = 0. We don't have quite this weak a typeclass, but
StarAddMonoid is close enough.
The StarAddMonoid class on C_c(α, β) is inherited from their counterparts on α →ᵇ β.
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The partial order in C_c #
When β is equipped with a partial order, C_c(α, β) is given the pointwise partial order.
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C_c as a functor #
For each β with sufficient structure, there is a contravariant functor C_c(-, β) from the
category of topological spaces with morphisms given by CocompactMaps.
Composition of a continuous function with compact support with a cocompact map yields another continuous function with compact support.
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Composition as an additive monoid homomorphism.
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Composition as a semigroup homomorphism.
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Composition as a linear map.
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Composition as a non-unital algebra homomorphism.
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A continuous function on a compact space has automatically compact support. This is not an instance to avoid type class loops.
The nonnegative part of a bounded continuous ℝ-valued function as a bounded
continuous ℝ≥0-valued function.
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The compactly supported continuous ℝ≥0-valued function as a compactly supported ℝ-valued
function.
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The map toReal defined as a ℝ≥0-linear map.
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For a positive linear functional Λ : C_c(α, ℝ) → ℝ, define a ℝ≥0-linear map.
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For a positive linear functional Λ : C_c(α, ℝ≥0) → ℝ≥0, define a ℝ-linear map.