Opened 5 months ago

Closed 4 months ago

#27966 closed defect (fixed)

Set chromatic polynomial of looped graph to zero

Reported by: slelievre Owned by:
Priority: major Milestone: sage-8.9
Component: graph theory Keywords: beginner
Cc: slelievre, dcoudert Merged in:
Authors: Matt Torrence Reviewers: Samuel Lelièvre
Report Upstream: N/A Work issues:
Branch: e7e5e8a (Commits) Commit: e7e5e8aba566951b4244399e31b4f81a8c187658
Dependencies: Stopgaps:

Description (last modified by slelievre)

The chromatic polynomial of a looped graph should be zero.

Initially reported by Ask Sage user "luis":

Change History (8)

comment:1 Changed 5 months ago by slelievre

  • Keywords beginner added

For anyone looking for a beginner ticket, this should be fairly easy.

comment:2 Changed 5 months ago by embray

  • Milestone sage-8.8 deleted

As the Sage-8.8 release milestone is pending, we should delete the sage-8.8 milestone for tickets that are not actively being worked on or that still require significant work to move forward. If you feel that this ticket should be included in the next Sage release at the soonest please set its milestone to the next release milestone (sage-8.9).

comment:3 Changed 5 months ago by dimpase

  • Cc dcoudert added
  • Milestone set to sage-8.9

OK, we can indeed check for presence of a loop, and set the chromatic number to 0.

comment:4 Changed 4 months ago by gh-Torrencem

  • Branch set to u/gh-Torrencem/27966_graph_loop_chrom
  • Commit set to e7e5e8aba566951b4244399e31b4f81a8c187658
  • Status changed from new to needs_review

This change updates G.chromatic_polynomial() to give 0 (in ZZ['x']). chromatic_number() already raises a ValueError when G has loops=True, so it isn't strictly necessary to change that.


New commits:

e7e5e8a27966: Chromatic Polynomial for graphs with loops is 0

comment:5 Changed 4 months ago by slelievre

  • Description modified (diff)
  • Summary changed from set chromatic number of looped graph to zero to Set chromatic polynomial of looped graph to zero

Please fill in author name.

comment:6 Changed 4 months ago by gh-Torrencem

  • Authors set to Matt Torrence

comment:7 Changed 4 months ago by slelievre

  • Description modified (diff)
  • Reviewers set to Samuel Lelièvre
  • Status changed from needs_review to positive_review

Thanks.

comment:8 Changed 4 months ago by vbraun

  • Branch changed from u/gh-Torrencem/27966_graph_loop_chrom to e7e5e8aba566951b4244399e31b4f81a8c187658
  • Resolution set to fixed
  • Status changed from positive_review to closed
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