#10670: Mobius matrices of posets are integer matrices
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Reporter: chapoton | Owner: sage-combinat
Type: defect | Status: needs_review
Priority: minor | Milestone:
Component: combinatorics | Keywords: poset, matrix
Work_issues: | Upstream: N/A
Reviewer: | Author: chapoton
Merged: | Dependencies:
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Description changed by chapoton:
Old description:
> I have noticed the following problem.
>
> {{{
> P=Posets.PentagonPoset()
> P.mobius_function_matrix().parent()
> Full MatrixSpace of 5 by 5 sparse matrices over Rational Field
> }}}
> The Mobius function of a poset should really be an '''integer matrix'''.
> This can be achieved by using change_ring :
>
> {{{
> P.mobius_function_matrix().change_ring(ZZ).parent()
> Full MatrixSpace of 5 by 5 sparse matrices over Integer Ring
> }}}
>
> The patch just does this be default.
New description:
I have noticed the following problem.
{{{
P=Posets.PentagonPoset()
P.mobius_function_matrix().parent()
Full MatrixSpace of 5 by 5 sparse matrices over Rational Field
}}}
The Mobius function of a poset should really be an '''integer matrix'''.
This can be achieved by using change_ring :
{{{
P.mobius_function_matrix().change_ring(ZZ).parent()
Full MatrixSpace of 5 by 5 sparse matrices over Integer Ring
}}}
The patch just does this by default.
Apply:
* [attachment:trac_10670_integral_mobius_matrix_for_posets-fc.patch]
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Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/10670#comment:5>
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