Locally integrable functions #
A function is called locally integrable (MeasureTheory.LocallyIntegrable) if it is integrable
on a neighborhood of every point. More generally, it is locally integrable on s if it is
locally integrable on a neighbourhood within s of any point of s.
This file contains properties of locally integrable functions, and integrability results on compact sets.
Main statements #
Continuous.locallyIntegrable: A continuous function is locally integrable.ContinuousOn.locallyIntegrableOn: A function which is continuous onsis locally integrable ons.
A function f : X → E is locally integrable on s, for s ⊆ X, if for every x ∈ s there is
a neighbourhood of x within s on which f is integrable. (Note this is, in general, strictly
weaker than local integrability with respect to μ.restrict s.)
Equations
- MeasureTheory.LocallyIntegrableOn f s μ = ∀ x ∈ s, MeasureTheory.IntegrableAtFilter f (nhdsWithin x s) μ
Instances For
If a function is locally integrable on a compact set, then it is integrable on that set.
If a function f is locally integrable on a set s in a second countable topological space,
then there exist countably many open sets u covering s such that f is integrable on each
set u ∩ s.
If a function f is locally integrable on a set s in a second countable topological space,
then there exists a sequence of open sets u n covering s such that f is integrable on each
set u n ∩ s.
If s is locally closed (e.g. open or closed), then f is locally integrable on s iff it is
integrable on every compact subset contained in s.
A function f : X → ε is locally integrable if it is integrable on a neighborhood of every
point. In particular, it is integrable on all compact sets,
see LocallyIntegrable.integrableOn_isCompact.
Equations
- MeasureTheory.LocallyIntegrable f μ = ∀ (x : X), MeasureTheory.IntegrableAtFilter f (nhds x) μ
Instances For
If f is locally integrable with respect to μ.restrict s, it is locally integrable on s.
(See locallyIntegrableOn_iff_locallyIntegrable_restrict for an iff statement when s is
closed.)
If s is closed, being locally integrable on s w.r.t. μ is equivalent to being locally
integrable with respect to μ.restrict s. For the one-way implication without assuming s closed,
see locallyIntegrableOn_of_locallyIntegrable_restrict.
If a function is locally integrable, then it is integrable on any compact set.
If a function is locally integrable, then it is integrable on an open neighborhood of any compact set.
If a function is locally integrable in a second countable topological space, then there exists a sequence of open sets covering the space on which it is integrable.
If f is locally integrable and g is continuous with compact support,
then g • f is integrable.
If f is locally integrable and g is continuous with compact support,
then f • g is integrable.
A continuous function f is locally integrable with respect to any locally finite measure.
A function f continuous on a set K is locally integrable on this set with respect
to any locally finite measure.
A function f continuous on a compact set K is integrable on this set with respect to any
locally finite measure.
A continuous function with compact support is integrable on the whole space.