#16237: IncidenceStructureFromMatrix bug
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Reporter: knsam | Owner:
Type: PLEASE CHANGE | Status: new
Priority: major | Milestone: sage-6.2
Component: PLEASE CHANGE | Keywords:
Merged in: | Authors:
Reviewers: | Report Upstream: N/A
Work issues: | Branch:
Commit: | Dependencies:
Stopgaps: |
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The method IncidenceStructureFromMatrix has a serious bug, and it leads to
serious errors in computations. We should fix it ASAP. For example, one
may test with HadamardDesign (which uses the buggy implementation of
IncidenceStructureFromMatrix). Consider the following output:
{{{
sage: D = designs.HadamardDesign(11); N = D.incidence_matrix()
sage: J = matrix(ZZ, 11, 11, [1]*11*11); N*J
[6 6 6 6 6 6 6 6 6 6 6]
[6 6 6 6 6 6 6 6 6 6 6]
[6 6 6 6 6 6 6 6 6 6 6]
[6 6 6 6 6 6 6 6 6 6 6]
[6 6 6 6 6 6 6 6 6 6 6]
[5 5 5 5 5 5 5 5 5 5 5]
[4 4 4 4 4 4 4 4 4 4 4]
[4 4 4 4 4 4 4 4 4 4 4]
[4 4 4 4 4 4 4 4 4 4 4]
[4 4 4 4 4 4 4 4 4 4 4]
[4 4 4 4 4 4 4 4 4 4 4]
}}}
The bug is the indexing used in the if-testing in the method.
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Ticket URL: <http://trac.sagemath.org/ticket/16237>
Sage <http://www.sagemath.org>
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