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

Priority:  major  Milestone:  sage8.9 
Component:  graph theory  Keywords:  beginner 
Cc:  Samuel Lelièvre, David Coudert  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 

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:  David Coudert added 

Milestone:  → 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:  → u/ghTorrencem/27966_graph_loop_chrom 

Commit:  → e7e5e8aba566951b4244399e31b4f81a8c187658 
Status:  new → 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:  set chromatic number of looped graph to zero → Set chromatic polynomial of looped graph to zero 
Please fill in author name.
comment:6 Changed 3 years ago by
Authors:  → Matt Torrence 

comment:7 Changed 3 years ago by
Description:  modified (diff) 

Reviewers:  → Samuel Lelièvre 
Status:  needs_review → positive_review 
Thanks.
comment:8 Changed 3 years ago by
Branch:  u/ghTorrencem/27966_graph_loop_chrom → e7e5e8aba566951b4244399e31b4f81a8c187658 

Resolution:  → fixed 
Status:  positive_review → closed 
For anyone looking for a beginner ticket, this should be fairly easy.