Opened 3 years ago
Closed 3 years ago
#27966 closed defect (fixed)
Set chromatic polynomial of looped graph to zero
Reported by:  slelievre  Owned by:  

Priority:  major  Milestone:  sage8.9 
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, GitHub, GitLab)  Commit:  e7e5e8aba566951b4244399e31b4f81a8c187658 
Dependencies:  Stopgaps: 
Description (last modified by )
The chromatic polynomial of a looped graph should be zero.
Initially reported by Ask Sage user "luis":
Change History (8)
comment:1 Changed 3 years ago by
 Keywords beginner added
comment:2 Changed 3 years ago by
 Milestone sage8.8 deleted
As the Sage8.8 release milestone is pending, we should delete the sage8.8 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 (sage8.9).
comment:3 Changed 3 years ago by
 Cc dcoudert added
 Milestone set to sage8.9
OK, we can indeed check for presence of a loop, and set the chromatic number to 0.
comment:4 Changed 3 years ago by
 Branch set to u/ghTorrencem/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:
e7e5e8a  27966: Chromatic Polynomial for graphs with loops is 0

comment:5 Changed 3 years ago by
 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 3 years ago by
comment:7 Changed 3 years ago by
 Description modified (diff)
 Reviewers set to Samuel Lelièvre
 Status changed from needs_review to positive_review
Thanks.
comment:8 Changed 3 years ago by
 Branch changed from u/ghTorrencem/27966_graph_loop_chrom to e7e5e8aba566951b4244399e31b4f81a8c187658
 Resolution set to fixed
 Status changed from positive_review to closed
For anyone looking for a beginner ticket, this should be fairly easy.