#15836: BasisMatroid.circuits() returns a malformed SetSystem when called on the
empty matroid
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Reporter: Rudi | Owner:
Type: defect | Status: new
Priority: minor | Milestone: sage-6.2
Component: matroid theory | Keywords:
Merged in: | Authors:
Reviewers: | Report Upstream: N/A
Work issues: | Branch:
Commit: | Dependencies:
Stopgaps: |
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The following produces an error:
{{{
from sage.matroids.advanced import *
M=Basismatroid(groundset=[], rank =0)
for C in M.circuits(): print C
}}}
Also, len(M.circuits()) is reported to be 1, whereas len(M.cocircuits())
is 0 and the latter is not malformed.
It is a bit of a theological issue, but I think we agree that the matroid
on zero elements has circuits nor cocircuits:
in general a matroid of rank 0 on k elements has k circuits and no
cocircuits.
So I want to make sure that M.circuits() returns that empty SetSystem
(easy enough) but I also want to find out how it is possible that the
SetSystem becomes malformed in this case.
--
Ticket URL: <http://trac.sagemath.org/ticket/15836>
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