ℒp space #
This file describes properties of almost everywhere strongly measurable functions with finite
p-seminorm, denoted by snorm f p μ and defined for p:ℝ≥0∞ as 0 if p=0,
(∫ ‖f a‖^p ∂μ) ^ (1/p) for 0 < p < ∞ and essSup ‖f‖ μ for p=∞.
The Prop-valued Memℒp f p μ states that a function f : α → E has finite p-seminorm
and is almost everywhere strongly measurable.
Main definitions #
-
snorm' f p μ:(∫ ‖f a‖^p ∂μ) ^ (1/p)forf : α → Fandp : ℝ, whereαis a measurable space andFis a normed group. -
snormEssSup f μ: seminorm inℒ∞, equal to the essential supremumess_sup ‖f‖ μ. -
snorm f p μ: forp : ℝ≥0∞, seminorm inℒp, equal to0forp=0, tosnorm' f p μfor0 < p < ∞and tosnormEssSup f μforp = ∞. -
Memℒp f p μ: property that the functionfis almost everywhere strongly measurable and has finitep-seminorm for the measureμ(snorm f p μ < ∞)
ℒp seminorm #
We define the ℒp seminorm, denoted by snorm f p μ. For real p, it is given by an integral
formula (for which we use the notation snorm' f p μ), and for p = ∞ it is the essential
supremum (for which we use the notation snormEssSup f μ).
We also define a predicate Memℒp f p μ, requesting that a function is almost everywhere
measurable and has finite snorm f p μ.
This paragraph is devoted to the basic properties of these definitions. It is constructed as
follows: for a given property, we prove it for snorm' and snormEssSup when it makes sense,
deduce it for snorm, and translate it in terms of Memℒp.
(∫ ‖f a‖^q ∂μ) ^ (1/q), which is a seminorm on the space of measurable functions for which
this quantity is finite
Instances For
seminorm for ℒ∞, equal to the essential supremum of ‖f‖.
Equations
- MeasureTheory.snormEssSup f μ = essSup (fun x => ↑‖f x‖₊) μ
Instances For
ℒp seminorm, equal to 0 for p=0, to (∫ ‖f a‖^p ∂μ) ^ (1/p) for 0 < p < ∞ and to
essSup ‖f‖ μ for p = ∞.
Equations
- MeasureTheory.snorm f p μ = if p = 0 then 0 else if p = ⊤ then MeasureTheory.snormEssSup f μ else MeasureTheory.snorm' f (ENNReal.toReal p) μ
Instances For
The property that f:α→E is ae strongly measurable and (∫ ‖f a‖^p ∂μ)^(1/p) is finite
if p < ∞, or essSup f < ∞ if p = ∞.
Equations
- MeasureTheory.Memℒp f p = (MeasureTheory.AEStronglyMeasurable f μ ∧ MeasureTheory.snorm f p μ < ⊤)
Instances For
Alias of MeasureTheory.Memℒp.of_le.
A constant for the inequality ‖f + g‖_{L^p} ≤ C * (‖f‖_{L^p} + ‖g‖_{L^p}). It is equal to 1
for p ≥ 1 or p = 0, and 2^(1/p-1) in the more tricky interval (0, 1).
Equations
- MeasureTheory.LpAddConst p = if p ∈ Set.Ioo 0 1 then 2 ^ (1 / ENNReal.toReal p - 1) else 1
Instances For
Technical lemma to control the addition of functions in L^p even for p < 1: Given δ > 0,
there exists η such that two functions bounded by η in L^p have a sum bounded by δ. One
could take η = δ / 2 for p ≥ 1, but the point of the lemma is that it works also for p < 1.
A version of Markov's inequality using Lp-norms.
When c is negative, ‖f x‖ ≤ c * ‖g x‖ is nonsense and forces both f and g to have an
snorm of 0.
Hölder's inequality, as an inequality on the ℒp seminorm of an elementwise operation
fun x => b (f x) (g x).
Hölder's inequality, as an inequality on the ℒp seminorm of an elementwise operation
fun x => b (f x) (g x).
Bounded actions by normed rings #
In this section we show inequalities on the norm.
Hölder's inequality, as an inequality on the ℒp seminorm of a scalar product φ • f.
Bounded actions by normed division rings #
The inequalities in the previous section are now tight.
A continuous function with compact support belongs to L^∞.