Opened 6 years ago

Closed 6 years ago

#20980 closed enhancement (wontfix)

LatticePoset: certificate for non-modularity, part 1

Reported by: jmantysalo Owned by:
Priority: major Milestone: sage-duplicate/invalid/wontfix
Component: combinatorics Keywords:
Cc: tscrim, kdilks Merged in:
Authors: Jori Mäntysalo Reviewers: Kevin Dilks
Report Upstream: N/A Work issues: rebase over 7.3.beta7
Branch: public/test_branch_find_pentagon (Commits, GitHub, GitLab) Commit: 6043924acb37777cf7daa5f8a143d31d85bfd817
Dependencies: Stopgaps:

Status badges

Description

This patch will add a function to get a pentagon sublattice, if it exists.

Interface part of this will be certificate-options to functions checking if a lattice is (semi)modular.

Change History (16)

comment:1 Changed 6 years ago by jmantysalo

  • Branch set to u/jmantysalo/find_pentagon

comment:2 Changed 6 years ago by jmantysalo

  • Authors set to Jori Mäntysalo
  • Cc tscrim kdilks added
  • Commit set to f2f8925ddd093a4aa07d789a8a05bdd192b11282
  • Status changed from new to needs_review

Part of "add certificates" -serie. I guess that this is useful for teaching at least.

But what did I wrong? The patch seems to work, but Branch-field is red.


New commits:

f2f8925Add functions to search pentagon sublattice.

comment:3 Changed 6 years ago by dimpase

  • Cc dimpase added

comment:4 Changed 6 years ago by dimpase

  • Branch changed from u/jmantysalo/find_pentagon to u/jmantysalo/_pentagon
  • Cc dimpase removed
  • Commit f2f8925ddd093a4aa07d789a8a05bdd192b11282 deleted

comment:5 Changed 6 years ago by dimpase

  • Branch changed from u/jmantysalo/_pentagon to u/jmantysalo/find_pentagon
  • Commit set to f2f8925ddd093a4aa07d789a8a05bdd192b11282

New commits:

f2f8925Add functions to search pentagon sublattice.

comment:6 Changed 6 years ago by dimpase

  • Branch changed from u/jmantysalo/find_pentagon to public/test_branch_find_pentagon
  • Commit changed from f2f8925ddd093a4aa07d789a8a05bdd192b11282 to 85bc0252c39d0a3e0769fd6b1d51a7e17e0814c4

New commits:

85bc025add a space in a comment, to change the file

comment:7 Changed 6 years ago by dimpase

  • Status changed from needs_review to needs_work
  • Work issues set to rebase over 7.3.beta7

we live in the future :-)

comment:8 Changed 6 years ago by git

  • Commit changed from 85bc0252c39d0a3e0769fd6b1d51a7e17e0814c4 to 6043924acb37777cf7daa5f8a143d31d85bfd817

Branch pushed to git repo; I updated commit sha1. This was a forced push. New commits:

6043924Add pentagon sublattice search.

comment:9 Changed 6 years ago by jmantysalo

  • Status changed from needs_work to needs_review

Hooray! Green link!

comment:10 Changed 6 years ago by kdilks

Ok, I've spent a bit of time convincing myself the math works out with the description, and I think it needs some clarification.

Strictly speaking, what the description mentions corresponds to Birkhoff's condition for weak semimodularity. Just looking at the definition of semimodularity, it appears one only needs a pair of elements a and b so that a covers the meet and b is not covered by the join. It's only because weakly semimodular is equivalent to semimodular for finite lattices* that we can further require that b covers the meet and a is covered by the join.

*(technically lattices of finite length and upper continuous relatively atomic lattices...whatever that means)

comment:11 Changed 6 years ago by jmantysalo

True, minimal certificate for non-semimodularity would be two elements. They can be extracted from this pentagon.

What about non-modular and non-distributive lattices? Should we return elements (a, b, x) violating definition of modularity, and same with distributivity?

After this we could think about best implementation. Maybe is_distributive(certificate=True) should first call is_modular(certificate=True) which could call is_upper_semimodular() and is_lower(semimodular). But if a non-distributive lattice is modular, then is_distributive() runs it's own subprogram to find the three elements of M_3 sublattice.

comment:12 follow-up: Changed 6 years ago by jmantysalo

  • Milestone changed from sage-7.3 to sage-duplicate/invalid/wontfix

#21002 kind of overrides this, so I think this one can be closed.

comment:13 in reply to: ↑ 12 Changed 6 years ago by jmantysalo

Replying to jmantysalo:

#21002 kind of overrides this, so I think this one can be closed.

Kevin, just asking confirmation for this.

comment:14 follow-up: Changed 6 years ago by kdilks

  • Reviewers set to Kevin Dilks
  • Status changed from needs_review to positive_review

Didn't realize I needed to do a thing for person reporting/authoring a ticket setting it to wontfix.

comment:15 in reply to: ↑ 14 Changed 6 years ago by jmantysalo

Replying to kdilks:

Didn't realize I needed to do a thing for person reporting/authoring a ticket setting it to wontfix.

Well, I don't know if it's really meaningful for tickets like this. I have just used to ask confirmation for even wontfixes, see #5964 as a trivial example.

comment:16 Changed 6 years ago by embray

  • Resolution set to wontfix
  • Status changed from positive_review to closed

Determined to be invalid/duplicate/wontfix (closing as "wontfix" as a catch-all resolution).

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