#15189: LinearMatroid.is_field_isomorphic fails on some occasions
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Reporter: Stefan | Owner:
Type: defect | Status: needs_review
Priority: major | Milestone: sage-5.12
Component: matroid theory | Resolution:
Keywords: | Merged in:
Authors: Stefan van Zwam | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
Dependencies: | Stopgaps:
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Changes (by {'newvalue': u'Stefan van Zwam', 'oldvalue': ''}):
* status: needs_work => needs_review
* author: => Stefan van Zwam
Old description:
> The following code should return False:
> {{{
> sage: M = Matroid(ring=GF(5), reduced_matrix=[[1,0,3],[0,1,1],[1,1,0]])
> sage: N = Matroid(ring=GF(5), reduced_matrix=[[1,0,1],[0,1,1],[1,1,0]])
> sage: M.is_field_isomorphic(N)
> True
> }}}
>
> Indeed:
>
> {{{
> sage: any(M.is_field_isomorphism(N, p) for p in Permutations(range(6)))
> False
> }}}
>
> The cause is a recursive call gone wrong in set_system.pyx.
New description:
The following code should return False:
{{{
sage: M = Matroid(ring=GF(5), reduced_matrix=[[1,0,3],[0,1,1],[1,1,0]])
sage: N = Matroid(ring=GF(5), reduced_matrix=[[1,0,1],[0,1,1],[1,1,0]])
sage: M.is_field_isomorphic(N)
True
}}}
Indeed:
{{{
sage: any(M.is_field_isomorphism(N, p) for p in Permutations(range(6)))
False
}}}
The cause is a recursive call gone wrong in set_system.pyx.
apply trac_15189_field_isom_fix.patch
--
Comment:
Ok, I chickened out of the Git development process for now and uploaded a
good, old-fashioned patch.
--
Ticket URL: <http://trac.sagemath.org/ticket/15189#comment:7>
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