Schwartz space #
This file defines the Schwartz space. Usually, the Schwartz space is defined as the set of smooth
functions $f : β^n β β$ such that there exists $C_{Ξ±Ξ²} > 0$ with $$|x^Ξ± β^Ξ² f(x)| < C_{Ξ±Ξ²}$$ for
all $x β β^n$ and for all multiindices $Ξ±, Ξ²$.
In mathlib, we use a slightly different approach and define the Schwartz space as all
smooth functions f : E β F, where E and F are real normed vector spaces such that for all
natural numbers k and n we have uniform bounds βxβ ^ k * βiteratedFDeriv β n f xβ < C.
This approach completely avoids using partial derivatives as well as polynomials.
We construct the topology on the Schwartz space by a family of seminorms, which are the best
constants in the above estimates. The abstract theory of topological vector spaces developed in
SeminormFamily.moduleFilterBasis and WithSeminorms.toLocallyConvexSpace turns the
Schwartz space into a locally convex topological vector space.
Main definitions #
SchwartzMap: The Schwartz space is the space of smooth functions such that all derivatives decay faster than any power ofβxβ.SchwartzMap.seminorm: The family of seminorms as described aboveSchwartzMap.compCLM: Composition with a function on the right as a continuous linear mapπ’(E, F) βL[π] π’(D, F), provided that the function is temperate and grows polynomially near infinitySchwartzMap.integralCLM: Integration as a continuous linear mapπ’(β, F) βL[β] F
Main statements #
SchwartzMap.instIsUniformAddGroupandSchwartzMap.instLocallyConvexSpace: The Schwartz space is a locally convex topological vector space.SchwartzMap.one_add_le_sup_seminorm_apply: For a Schwartz functionfthere is a uniform bound on(1 + βxβ) ^ k * βiteratedFDeriv β n f xβ.
Implementation details #
The implementation of the seminorms is taken almost literally from ContinuousLinearMap.opNorm.
Notation #
π’(E, F): The Schwartz spaceSchwartzMap E Flocalized inSchwartzSpace
Tags #
Schwartz space, tempered distributions
A function is a Schwartz function if it is smooth and all derivatives decay faster than
any power of βxβ.
- toFun : E β F
The underlying function.
Do NOT use directly. Use the coercion instead.
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A function is a Schwartz function if it is smooth and all derivatives decay faster than
any power of βxβ.
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All derivatives of a Schwartz function are rapidly decaying.
Every Schwartz function is smooth.
Every Schwartz function is smooth at any point.
Every Schwartz function is continuous.
Every Schwartz function is differentiable.
Every Schwartz function is differentiable at any point.
Auxiliary lemma, used in proving the more general result isBigO_cocompact_rpow.
Algebraic properties #
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Coercion as an additive homomorphism.
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Seminorms on Schwartz space #
The seminorms of the Schwartz space given by the best constants in the definition of
π’(E, F).
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The seminorm is given by infimum over all c such that the estimate
βxβ ^ k * βiteratedFDeriv β n f xβ β€ c holds.
Note that it is usually better to use seminorm_le_bound or le_seminorm instead of this lemma.
If one controls the seminorm for every x, then one controls the seminorm.
If one controls the seminorm for every x, then one controls the seminorm.
Variant for functions π’(β, F).
The seminorm controls the Schwartz estimate for any fixed x.
The seminorm controls the Schwartz estimate for any fixed x.
Variant for functions π’(β, F).
The family of Schwartz seminorms.
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A more convenient version of le_sup_seminorm_apply.
The set Finset.Iic m is the set of all pairs (k', n') with k' β€ m.1 and n' β€ m.2.
Note that the constant is far from optimal.
The topology on the Schwartz space #
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A smooth compactly supported function is a Schwartz function.
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Construction of continuous linear maps between Schwartz spaces #
Create a semilinear map between Schwartz spaces.
Note: This is a helper definition for mkCLM.
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Create a continuous semilinear map between Schwartz spaces.
For an example of using this definition, see fderivCLM.
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Define a continuous semilinear map from Schwartz space to a normed space.
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The map applying a vector to Hom-valued Schwartz function as a continuous linear map.
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The map f β¦ (x β¦ B (f x) (g x)) as a continuous π-linear map on Schwartz space,
where B is a continuous π-linear map and g is a function of temperate growth.
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The map f β¦ (x β¦ g x β’ f x) as a continuous π-linear map on Schwartz space,
where g is a function of temperate growth.
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The bilinear pairing of Schwartz functions.
The continuity in the left argument is provided in SchwartzMap.pairing_continuous_left.
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The pairing is continuous in the left argument.
Note that since π’(E, F) is not a normed space, uncurried and curried continuity do not
coincide.
Scalar multiplication with a continuous linear map as a continuous linear map on Schwartz functions.
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Composition with a function on the right is a continuous linear map on Schwartz space provided that the function is temperate and growths polynomially near infinity.
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Composition with a function on the right is a continuous linear map on Schwartz space provided that the function is temperate and antilipschitz.
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Composition with a continuous linear equiv on the right is a continuous linear map on Schwartz space.
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Integration #
The integral as a continuous linear map from Schwartz space to the codomain.
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Inclusion into the space of bounded continuous functions #
Schwartz functions as bounded continuous functions
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Schwartz functions as continuous functions
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The inclusion map from Schwartz functions to bounded continuous functions as a continuous linear map.
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Schwartz functions as continuous functions vanishing at infinity.
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The inclusion map from Schwartz functions to continuous functions vanishing at infinity as a continuous linear map.
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Inclusion into L^p space #
The L^p norm of a Schwartz function is controlled by a finite family of Schwartz seminorms.
The maximum index k and the constant C depend on p and ΞΌ.
The L^p norm of a Schwartz function is finite.
Schwartz functions are in L^β; does not require hΞΌ.HasTemperateGrowth.
Schwartz functions are in L^p for any p.
Map a Schwartz function to an Lp function for any p.
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Continuous linear map from Schwartz functions to L^p.
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Schwartz functions are dense in Lp.