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 → F
andp : ℝ
, whereα
is a measurable space andF
is 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 to0
forp=0
, tosnorm' f p μ
for0 < p < ∞
and tosnormEssSup f μ
forp = ∞
. -
Memℒp f p μ
: property that the functionf
is 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 : α) => ↑‖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^∞
.