#17658: Incorrect densification of polynomial matrix
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Reporter: gagern | Owner:
Type: defect | Status: new
Priority: critical | Milestone: sage-6.5
Component: linear algebra | Keywords:
Merged in: | Authors:
Reviewers: | Report Upstream: N/A
Work issues: | Branch:
Commit: | Dependencies:
Stopgaps: |
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I found this strange bug, trying to turn a sparse matrix into a dense one.
{{{
sage: R1.<a,b> = QQ[]
sage: R2.<c,d> = R1[]
sage: p = a*c+b*d
sage: d = dict(zip([i.degrees() for i in p.monomials()],
p.coefficients()))
sage: m = matrix(R1, 2, 2, d)
sage: m
[0 b]
[a 0]
sage: m.dense_matrix()
[0 0]
[0 0]
}}}
For some reason the source of the matrix entries seems to play a role here
as well: if I simply type in the dict `d` directly, the result works as
expected. So I'm not at all sure what actual component is to blame for
this behavior. Omitting the two levels of polynomials, and using QQ for
the coefficients, doesn't exhibit this problem either.
Since this can lead to silent wrong answers, I consider this a critical
problem.
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Ticket URL: <http://trac.sagemath.org/ticket/17658>
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