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[Merged by Bors] - feat: prove the Gagliardo-Nirenberg-Sobolev inequality #14165
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PR summary 809a3c5646Import changesNo significant changes to the import graph
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This PR/issue depends on: |
@@ -672,6 +672,13 @@ theorem memℒp_indicator_iff_restrict (hs : MeasurableSet s) : | |||
simp [Memℒp, aestronglyMeasurable_indicator_iff hs, snorm_indicator_eq_snorm_restrict hs] | |||
#align measure_theory.mem_ℒp_indicator_iff_restrict MeasureTheory.memℒp_indicator_iff_restrict | |||
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/-- For a function `f` with support in `s`, the Lᵖ norms of `f` with respect to `μ` and | |||
`μ.restrict s` are the same. -/ | |||
theorem snorm_restrict_eq {s : Set α} (hs : MeasurableSet s) (hsf : f.support ⊆ s) : |
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hs shouldn't be needed: otherwise, use the measurable hull of s instead. Since it contains s, it will also satisfy hsf
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I also thought that, but I wasn't sure how to get snorm f p (μ.restrict s) = snorm f p (μ.restrict (toMeasurable μ s))
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Loogle tells me about MeasureTheory.Measure.restrict_toMeasurable_of_sFinite
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I can replace (hs : MeasurableSet s)
by [SFinite μ]
. Do you think that is better? Both are true in my application.
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I replaced the lemma, and this is actually nicer. I didn't realize we had to put some effort in making the set measurable when we applied it, so this is a nice simplification.
This does add a small amount of imports to the file LpSpace
.
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I have a proof removing the SFinite
assumption, but I will first wait for #14260 to be merged, to avoid introducing new lemmas with a wrong name.
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See #14289
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It feels weird to have this in the MeasureTheory folder; this is firmly a statement in analysis, just like all Sobolev spaces theory. Maybe create a folder Analysis/FunctionalSpaces
and put it there?
@@ -672,6 +673,15 @@ theorem memℒp_indicator_iff_restrict (hs : MeasurableSet s) : | |||
simp [Memℒp, aestronglyMeasurable_indicator_iff hs, snorm_indicator_eq_snorm_restrict hs] | |||
#align measure_theory.mem_ℒp_indicator_iff_restrict MeasureTheory.memℒp_indicator_iff_restrict | |||
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/-- For a function `f` with support in `s`, the Lᵖ norms of `f` with respect to `μ` and | |||
`μ.restrict s` are the same. -/ | |||
theorem snorm_restrict_eq [SFinite μ] {s : Set α} (hsf : f.support ⊆ s) : |
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In fact I think it's possible to get rid also of the SFinite condition, but I'll do that after this PR is merged.
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/-! ## The Gagliardo-Nirenberg-Sobolev inequality -/ | ||
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variable {F : Type*} [NormedAddCommGroup F] [NormedSpace ℝ F] [CompleteSpace F] |
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The completeness assumption here is probably not necessary, but removing this can definitely wait for another PR.
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Done in #14262
Thanks for your quick reviews! |
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bors d+
Thanks!
✌️ fpvandoorn can now approve this pull request. To approve and merge a pull request, simply reply with |
bors merge |
* From the Sobolev inequality project Co-authored-by: Heather Macbeth [email protected]
Pull request successfully merged into master. Build succeeded: |
* Forgot to incorporate 1 review comment from #14165
* From the Sobolev inequality project Co-authored-by: Heather Macbeth [email protected]
* Forgot to incorporate 1 review comment from #14165
Co-authored-by: Heather Macbeth [email protected]