Weak dual topology #
This file defines the weak topology given two vector spaces E and F over a commutative semiring
𝕜 and a bilinear form B : E →ₗ[𝕜] F →ₗ[𝕜] 𝕜. The weak topology on E is the coarsest topology
such that for all y : F every map fun x => B x y is continuous.
In the case that F = E →L[𝕜] 𝕜 and B being the canonical pairing, we obtain the weak-* topology,
WeakDual 𝕜 E := (E →L[𝕜] 𝕜). Interchanging the arguments in the bilinear form yields the
weak topology WeakSpace 𝕜 E := E.
Main definitions #
The main definitions are the types WeakBilin B for the general case and the two special cases
WeakDual 𝕜 E and WeakSpace 𝕜 E with the respective topology instances on it.
- Given
B : E →ₗ[𝕜] F →ₗ[𝕜] 𝕜, the typeWeakBilin Bis a type synonym forE. - The instance
WeakBilin.instTopologicalSpaceis the weak topology induced by the bilinear formB. WeakDual 𝕜 Eis a type synonym forDual 𝕜 E(when the latter is defined): both are equal to the typeE →L[𝕜] 𝕜of continuous linear maps from a moduleEover𝕜to the ring𝕜.- The instance
WeakDual.instTopologicalSpaceis the weak-* topology onWeakDual 𝕜 E, i.e., the coarsest topology making the evaluation maps at allz : Econtinuous. WeakSpace 𝕜 Eis a type synonym forE(when the latter is defined).- The instance
WeakSpace.instTopologicalSpaceis the weak topology onE, i.e., the coarsest topology such that allv : dual 𝕜 Eremain continuous.
Main results #
We establish that WeakBilin B has the following structure:
WeakBilin.instContinuousAdd: The addition inWeakBilin Bis continuous.WeakBilin.instContinuousSMul: The scalar multiplication inWeakBilin Bis continuous.
We prove the following results characterizing the weak topology:
eval_continuous: For anyy : F, the evaluation mappingfun x => B x yis continuous.continuous_of_continuous_eval: For a mapping toWeakBilin Bto be continuous, it suffices that its compositions with pairing withBat all pointsy : Fis continuous.tendsto_iff_forall_eval_tendsto: Convergence inWeakBilin Bcan be characterized in terms of convergence of the evaluations at all pointsy : F.
Notations #
No new notation is introduced.
References #
- [H. H. Schaefer, Topological Vector Spaces][schaefer1966]
Tags #
weak-star, weak dual, duality
Equations
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- ⋯ = s
Equations
- WeakBilin.instTopologicalSpace B = TopologicalSpace.induced (fun (x : WeakBilin B) (y : F) => (B x) y) Pi.topologicalSpace
The coercion (fun x y => B x y) : E → (F → 𝕜) is continuous.
The coercion (fun x y => B x y) : E → (F → 𝕜) is an embedding.
Addition in WeakBilin B is continuous.
Equations
- ⋯ = ⋯
Scalar multiplication by 𝕜 on WeakBilin B is continuous.
Equations
- ⋯ = ⋯
WeakBilin B is a TopologicalAddGroup, meaning that addition and negation are
continuous.
Equations
- ⋯ = ⋯
The canonical pairing of a vector space and its topological dual.
Equations
Instances For
The weak star topology is the topology coarsest topology on E →L[𝕜] 𝕜 such that all
functionals fun v => v x are continuous.
Equations
- WeakDual 𝕜 E = WeakBilin (topDualPairing 𝕜 E)
Instances For
Equations
- WeakDual.instAddCommMonoid = WeakBilin.instAddCommMonoid (topDualPairing 𝕜 E)
Equations
- WeakDual.instModule = WeakBilin.instModule (topDualPairing 𝕜 E)
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- WeakDual.instTopologicalSpace = WeakBilin.instTopologicalSpace (topDualPairing 𝕜 E)
Equations
- ⋯ = ⋯
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- WeakDual.instInhabited = ContinuousLinearMap.inhabited
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- WeakDual.instFunLike = ContinuousLinearMap.funLike
Equations
- ⋯ = ⋯
Helper instance for when there's too many metavariables to apply DFunLike.hasCoeToFun
directly.
Equations
- WeakDual.instCoeFunWeakDualForAll = DFunLike.hasCoeToFun
If a monoid M distributively continuously acts on 𝕜 and this action commutes with
multiplication on 𝕜, then it acts on WeakDual 𝕜 E.
Equations
- WeakDual.instMulAction M = ContinuousLinearMap.mulAction
If a monoid M distributively continuously acts on 𝕜 and this action commutes with
multiplication on 𝕜, then it acts distributively on WeakDual 𝕜 E.
Equations
- WeakDual.instDistribMulAction M = ContinuousLinearMap.distribMulAction
If 𝕜 is a topological module over a semiring R and scalar multiplication commutes with the
multiplication on 𝕜, then WeakDual 𝕜 E is a module over R.
Equations
- WeakDual.instModule' R = ContinuousLinearMap.module
Equations
- ⋯ = ⋯
If a monoid M distributively continuously acts on 𝕜 and this action commutes with
multiplication on 𝕜, then it continuously acts on WeakDual 𝕜 E.
Equations
- ⋯ = ⋯
Equations
- ⋯ = ⋯
The weak topology is the topology coarsest topology on E such that all functionals
fun x => v x are continuous.
Equations
- WeakSpace 𝕜 E = WeakBilin (LinearMap.flip (topDualPairing 𝕜 E))
Instances For
Equations
- WeakSpace.instAddCommMonoid = WeakBilin.instAddCommMonoid (LinearMap.flip (topDualPairing 𝕜 E))
Equations
- WeakSpace.instModule = WeakBilin.instModule (LinearMap.flip (topDualPairing 𝕜 E))
Equations
- WeakSpace.instTopologicalSpace = WeakBilin.instTopologicalSpace (LinearMap.flip (topDualPairing 𝕜 E))
Equations
- ⋯ = ⋯
A continuous linear map from E to F is still continuous when E and F are equipped with
their weak topologies.
Equations
- WeakSpace.map f = { toLinearMap := ↑f, cont := ⋯ }