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 B
is a type synonym forE
. - The instance
WeakBilin.instTopologicalSpace
is the weak topology induced by the bilinear formB
. WeakDual 𝕜 E
is a type synonym forDual 𝕜 E
(when the latter is defined): both are equal to the typeE →L[𝕜] 𝕜
of continuous linear maps from a moduleE
over𝕜
to the ring𝕜
.- The instance
WeakDual.instTopologicalSpace
is the weak-* topology onWeakDual 𝕜 E
, i.e., the coarsest topology making the evaluation maps at allz : E
continuous. WeakSpace 𝕜 E
is a type synonym forE
(when the latter is defined).- The instance
WeakSpace.instTopologicalSpace
is the weak topology onE
, i.e., the coarsest topology such that allv : dual 𝕜 E
remain continuous.
Main results #
We establish that WeakBilin B
has the following structure:
WeakBilin.instContinuousAdd
: The addition inWeakBilin B
is continuous.WeakBilin.instContinuousSMul
: The scalar multiplication inWeakBilin B
is continuous.
We prove the following results characterizing the weak topology:
eval_continuous
: For anyy : F
, the evaluation mappingfun x => B x y
is continuous.continuous_of_continuous_eval
: For a mapping toWeakBilin B
to be continuous, it suffices that its compositions with pairing withB
at all pointsy : F
is continuous.tendsto_iff_forall_eval_tendsto
: Convergence inWeakBilin B
can 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
Equations
Equations
Equations
Equations
- ⋯ = 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)
Equations
- WeakDual.instTopologicalSpace = WeakBilin.instTopologicalSpace (topDualPairing 𝕜 E)
Equations
- ⋯ = ⋯
Equations
- WeakDual.instInhabited = ContinuousLinearMap.inhabited
Equations
- WeakDual.instFunLike = ContinuousLinearMap.funLike
Equations
- ⋯ = ⋯
Helper instance for when there's too many metavariables to apply DFunLike.hasCoeToFun
directly.
Equations
- WeakDual.instCoeFunForall = 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 (topDualPairing 𝕜 E).flip
Instances For
Equations
- WeakSpace.instAddCommMonoid = WeakBilin.instAddCommMonoid (topDualPairing 𝕜 E).flip
Equations
- WeakSpace.instModule = WeakBilin.instModule (topDualPairing 𝕜 E).flip
Equations
- WeakSpace.instTopologicalSpace = WeakBilin.instTopologicalSpace (topDualPairing 𝕜 E).flip
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 := ⋯ }
Instances For
There is a canonical map E → WeakSpace 𝕜 E
(the "identity"
mapping). It is a linear equivalence.
Equations
- toWeakSpace 𝕜 E = LinearEquiv.refl 𝕜 E
Instances For
For a topological vector space E
, "identity mapping" E → WeakSpace 𝕜 E
is continuous.
This definition implements it as a continuous linear map.
Equations
- continuousLinearMapToWeakSpace 𝕜 E = let __spread.0 := toWeakSpace 𝕜 E; { toLinearMap := ↑__spread.0, cont := ⋯ }
Instances For
The canonical map from WeakSpace 𝕜 E
to E
is an open map.
A set in E
which is open in the weak topology is open.