ℓp space #
This file describes properties of elements f of a pi-type ∀ i, E i with finite "norm",
defined for p : ℝ≥0∞ as the size of the support of f if p=0, (∑' a, ‖f a‖^p) ^ (1/p) for
0 < p < ∞ and ⨆ a, ‖f a‖ for p=∞.
The Prop-valued Memℓp f p states that a function f : ∀ i, E i has finite norm according
to the above definition; that is, f has finite support if p = 0, Summable (fun a ↦ ‖f a‖^p) if
0 < p < ∞, and BddAbove (norm '' (Set.range f)) if p = ∞.
The space lp E p is the subtype of elements of ∀ i : α, E i which satisfy Memℓp f p. For
1 ≤ p, the "norm" is genuinely a norm and lp is a complete metric space.
Main definitions #
Memℓp f p: property that the functionfsatisfies, as appropriate,ffinitely supported ifp = 0,Summable (fun a ↦ ‖f a‖^p)if0 < p < ∞, andBddAbove (norm '' (Set.range f))ifp = ∞.lp E p: elements of∀ i : α, E isuch thatMemℓp f p. Defined as anAddSubgroupof a type synonymPreLpfor∀ i : α, E i, and equipped with aNormedAddCommGroupstructure. Under appropriate conditions, this is also equipped with the instanceslp.normedSpace,lp.completeSpace. Forp=∞, there is alsolp.inftyNormedRing,lp.inftyNormedAlgebra,lp.inftyStarRingandlp.inftyCStarRing.
Main results #
Memℓp.of_exponent_ge: Forq ≤ p, a function which isMemℓpforqis alsoMemℓpforp.lp.memℓp_of_tendsto,lp.norm_le_of_tendsto: A pointwise limit of functions inlp, all withlpnorm≤ C, is itself inlpand haslpnorm≤ C.lp.tsum_mul_le_mul_norm: basic form of Hölder's inequality
Implementation #
Since lp is defined as an AddSubgroup, dot notation does not work. Use lp.norm_neg f to
say that ‖-f‖ = ‖f‖, instead of the non-working f.norm_neg.
TODO #
- More versions of Hölder's inequality (for example: the case
p = 1,q = ∞; a version for normed rings which has‖∑' i, f i * g i‖rather than∑' i, ‖f i‖ * g i‖on the RHS; a version for three exponents satisfying1 / r = 1 / p + 1 / q)
The property that f : ∀ i : α, E i
- is finitely supported, if
p = 0, or - admits an upper bound for
Set.range (fun i ↦ ‖f i‖), ifp = ∞, or - has the series
∑' i, ‖f i‖ ^ pbe summable, if0 < p < ∞.
Equations
Instances For
We define PreLp E to be a type synonym for ∀ i, E i which, importantly, does not inherit
the pi topology on ∀ i, E i (otherwise this topology would descend to lp E p and conflict
with the normed group topology we will later equip it with.)
We choose to deal with this issue by making a type synonym for ∀ i, E i rather than for the lp
subgroup itself, because this allows all the spaces lp E p (for varying p) to be subgroups of
the same ambient group, which permits lemma statements like lp.monotone (below).
Instances For
Equations
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lp space
The p=∞ case has notation ℓ^∞(ι, E) resp. ℓ^∞(ι) (for E = ℝ) in the lp namespace.
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Instances For
lp space
The p=∞ case has notation ℓ^∞(ι, E) resp. ℓ^∞(ι) (for E = ℝ) in the lp namespace.
Equations
- One or more equations did not get rendered due to their size.
Instances For
lp space
The p=∞ case has notation ℓ^∞(ι, E) resp. ℓ^∞(ι) (for E = ℝ) in the lp namespace.
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- One or more equations did not get rendered due to their size.
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Coercion to function as an AddMonoidHom.
Equations
- lp.coeFnAddMonoidHom E p = { toFun := Subtype.val, map_zero' := ⋯, map_add' := ⋯ }
Instances For
Equations
- One or more equations did not get rendered due to their size.
Equations
- lp.normedAddCommGroup = { toFun := norm, map_zero' := ⋯, add_le' := ⋯, neg' := ⋯, eq_zero_of_map_eq_zero' := ⋯ }.toNormedAddCommGroup
Hölder inequality
Equations
- lp.instModulePreLp = Pi.module α E 𝕜
The 𝕜-submodule of elements of ∀ i : α, E i whose lp norm is finite. This is lp E p,
with extra structure.
Equations
- lpSubmodule 𝕜 E p = { toAddSubmonoid := (lp E p).toAddSubmonoid, smul_mem' := ⋯ }
Instances For
Equations
Equations
- lp.instNormedSpace = { toModule := lp.instModuleSubtypePreLpMemAddSubgroup, norm_smul_le := ⋯ }
Equations
- lp.instInvolutiveStar = { toStar := lp.instStarSubtypePreLpMemAddSubgroup, star_involutive := ⋯ }
Equations
- lp.instStarAddMonoid = { toInvolutiveStar := lp.instInvolutiveStar, star_add := ⋯ }
Equations
- lp.nonUnitalRing = Function.Injective.nonUnitalRing CoeFun.coe ⋯ ⋯ ⋯ ⋯ ⋯ ⋯ ⋯ ⋯
Equations
- One or more equations did not get rendered due to their size.
Equations
- lp.nonUnitalNormedCommRing = { toNonUnitalNormedRing := lp.nonUnitalNormedRing, mul_comm := ⋯ }
Equations
- lp.inftyStarRing = { toInvolutiveStar := lp.instStarAddMonoid.toInvolutiveStar, star_mul := ⋯, star_add := ⋯ }
Equations
The 𝕜-subring of elements of ∀ i : α, B i whose lp norm is finite. This is lp E ∞,
with extra structure.
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Instances For
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Equations
- lp.inftyNormedRing = { toNorm := lp.nonUnitalNormedRing.toNorm, toRing := lp.inftyRing, toMetricSpace := lp.nonUnitalNormedRing.toMetricSpace, dist_eq := ⋯, norm_mul_le := ⋯ }
Equations
- lp.inftyNormedCommRing = { toNormedRing := lp.inftyNormedRing, mul_comm := ⋯ }
A variant of Pi.algebra that lean can't find otherwise.
Equations
Equations
The 𝕜-subalgebra of elements of ∀ i : α, B i whose lp norm is finite. This is lp E ∞,
with extra structure.
Equations
Instances For
Equations
- lp.inftyNormedAlgebra = { toAlgebra := (lpInftySubalgebra 𝕜 B).algebra, norm_smul_le := ⋯ }
single as an AddMonoidHom.
Equations
- lp.singleAddMonoidHom p i = { toFun := lp.single p i, map_zero' := ⋯, map_add' := ⋯ }
Instances For
Equations
- lp.lsingle p i = { toFun := lp.single p i, map_add' := ⋯, map_smul' := ⋯ }
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lp.single as a continuous morphism of additive monoids.
Equations
- lp.singleContinuousAddMonoidHom E p i = { toAddMonoidHom := lp.singleAddMonoidHom p i, continuous_toFun := ⋯ }
Instances For
lp.single as a continuous linear map.
Equations
- lp.singleContinuousLinearMap 𝕜 E p i = { toLinearMap := lp.lsingle p i, cont := ⋯ }
Instances For
The canonical finitely-supported approximations to an element f of lp converge to it, in the
lp topology.
Two continuous additive maps from lp E p agree if they agree on lp.single.
See note [partially-applied ext lemmas].
Two continuous linear maps from lp E p agree if they agree on lp.single.
See note [partially-applied ext lemmas].
The coercion from lp E p to ∀ i, E i is uniformly continuous.
"Semicontinuity of the lp norm": If all sufficiently large elements of a sequence in lp E p
have lp norm ≤ C, then the pointwise limit, if it exists, also has lp norm ≤ C.
If f is the pointwise limit of a bounded sequence in lp E p, then f is in lp E p.
If a sequence is Cauchy in the lp E p topology and pointwise convergent to an element f of
lp E p, then it converges to f in the lp E p topology.