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[Merged by Bors] - feat(analysis/convex/caratheodory): strengthen Caratheodory's lemma to provide affine independence #8892

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@ocfnash ocfnash commented Aug 27, 2021

The changes here are:

  • Use hypothesis ¬ affine_independent ℝ (coe : t → E) instead of finrank ℝ E + 1 < t.card
  • Drop no-longer-necessary [finite_dimensional ℝ E] assumption
  • Do not use a shrinking argument but start by choosing an appropriate subset of minimum cardinality via min_card_finset_of_mem_convex_hull
  • Provide a single alternative form of Carathéodory's lemma eq_pos_convex_span_of_mem_convex_hull
  • In the alternate form, define the explicit linear combination using elements parameterised by a new fintype rather than on the entire ambient space E (we thus avoid the issue of junk values outside of the relevant subset)

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@ocfnash ocfnash added the WIP Work in progress label Aug 27, 2021
Evidently, these are just thin wrappers around `well_founded.min` but I think
this use case is common enough to deserve this specialisation.
@github-actions github-actions bot added the blocked-by-other-PR This PR depends on another PR which is still in the queue. A bot manages this label via PR comment. label Aug 27, 2021
@ocfnash ocfnash force-pushed the refined_caratheodory branch 2 times, most recently from a9887f8 to 3e533ab Compare August 30, 2021 11:41
@ocfnash ocfnash added awaiting-review The author would like community review of the PR and removed WIP Work in progress labels Aug 30, 2021
@github-actions github-actions bot removed the blocked-by-other-PR This PR depends on another PR which is still in the queue. A bot manages this label via PR comment. label Sep 1, 2021
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github-actions bot commented Sep 1, 2021

🎉 Great news! Looks like all the dependencies have been resolved:

💡 To add or remove a dependency please update this issue/PR description.

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@YaelDillies YaelDillies left a comment

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Thanks a lot for this!

Incidentally, I need this strenghtened Carathéodory for my next PR (convex independence). 😁

I particularly like the new explanation in the module docstring.

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Thanks 🎉

bors merge

@github-actions github-actions bot added ready-to-merge All that is left is for bors to build and merge this PR. (Remember you need to say `bors r+`.) and removed awaiting-review The author would like community review of the PR labels Sep 6, 2021
bors bot pushed a commit that referenced this pull request Sep 6, 2021
…o provide affine independence (#8892)

The changes here are:

- Use hypothesis `¬ affine_independent ℝ (coe : t → E)` instead of `finrank ℝ E + 1 < t.card`
- Drop no-longer-necessary `[finite_dimensional ℝ E]` assumption
- Do not use a shrinking argument but start by choosing an appropriate subset of minimum cardinality via `min_card_finset_of_mem_convex_hull`
- Provide a single alternative form of Carathéodory's lemma `eq_pos_convex_span_of_mem_convex_hull`
- In the alternate form, define the explicit linear combination using elements parameterised by a new `fintype` rather than on the entire ambient space `E` (we thus avoid the issue of junk values outside of the relevant subset)
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bors bot commented Sep 6, 2021

Build failed (retrying...):

bors bot pushed a commit that referenced this pull request Sep 6, 2021
…o provide affine independence (#8892)

The changes here are:

- Use hypothesis `¬ affine_independent ℝ (coe : t → E)` instead of `finrank ℝ E + 1 < t.card`
- Drop no-longer-necessary `[finite_dimensional ℝ E]` assumption
- Do not use a shrinking argument but start by choosing an appropriate subset of minimum cardinality via `min_card_finset_of_mem_convex_hull`
- Provide a single alternative form of Carathéodory's lemma `eq_pos_convex_span_of_mem_convex_hull`
- In the alternate form, define the explicit linear combination using elements parameterised by a new `fintype` rather than on the entire ambient space `E` (we thus avoid the issue of junk values outside of the relevant subset)
@bors
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bors bot commented Sep 6, 2021

Build failed (retrying...):

bors bot pushed a commit that referenced this pull request Sep 6, 2021
…o provide affine independence (#8892)

The changes here are:

- Use hypothesis `¬ affine_independent ℝ (coe : t → E)` instead of `finrank ℝ E + 1 < t.card`
- Drop no-longer-necessary `[finite_dimensional ℝ E]` assumption
- Do not use a shrinking argument but start by choosing an appropriate subset of minimum cardinality via `min_card_finset_of_mem_convex_hull`
- Provide a single alternative form of Carathéodory's lemma `eq_pos_convex_span_of_mem_convex_hull`
- In the alternate form, define the explicit linear combination using elements parameterised by a new `fintype` rather than on the entire ambient space `E` (we thus avoid the issue of junk values outside of the relevant subset)
@bors
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bors bot commented Sep 7, 2021

Build failed (retrying...):

bors bot pushed a commit that referenced this pull request Sep 7, 2021
…o provide affine independence (#8892)

The changes here are:

- Use hypothesis `¬ affine_independent ℝ (coe : t → E)` instead of `finrank ℝ E + 1 < t.card`
- Drop no-longer-necessary `[finite_dimensional ℝ E]` assumption
- Do not use a shrinking argument but start by choosing an appropriate subset of minimum cardinality via `min_card_finset_of_mem_convex_hull`
- Provide a single alternative form of Carathéodory's lemma `eq_pos_convex_span_of_mem_convex_hull`
- In the alternate form, define the explicit linear combination using elements parameterised by a new `fintype` rather than on the entire ambient space `E` (we thus avoid the issue of junk values outside of the relevant subset)
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bors bot commented Sep 7, 2021

Pull request successfully merged into master.

Build succeeded:

@bors bors bot changed the title feat(analysis/convex/caratheodory): strengthen Caratheodory's lemma to provide affine independence [Merged by Bors] - feat(analysis/convex/caratheodory): strengthen Caratheodory's lemma to provide affine independence Sep 7, 2021
@bors bors bot closed this Sep 7, 2021
@bors bors bot deleted the refined_caratheodory branch September 7, 2021 05:55
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