#15664: Bug in IncidenceStructure.is_block_design
-----------------------------+---------------------------------
Reporter: ncohen | Owner:
Type: defect | Status: new
Priority: major | Milestone: sage-6.1
Component: combinatorics | Keywords:
Merged in: | Authors: Nathann Cohen
Reviewers: | Report Upstream: N/A
Work issues: | Branch:
Commit: | Dependencies: #15285
Stopgaps: |
-----------------------------+---------------------------------
This bug has been noticed by Frederic in #15285 :
{{{
sage: IncidenceStructure([0,1,2],[[0,1],[0,2],[1,2]]*15).is_block_design()
(True, [1, 3, 2, 15])
sage: IncidenceStructure([0,1,2],[[0,1],[0,2],[1,2]]*15).parameters()
(2, 3, 2, 15)
}}}
Turns out that the code of `is_block_design` was rather unclear, and
rather... Costly. Here is a simpler, faster and more correct version in
which the bug in solved.
Before:
{{{
sage: D =
IncidenceStructure(range(32),designs.steiner_quadruple_system(32))
sage: time D.is_block_design()
CPU times: user 14.31 s, sys: 0.00 s, total: 14.32 s
Wall time: 14.33 s
(True, [3, 32, 4, 1])
}}}
After:
{{{
sage: D =
IncidenceStructure(range(32),designs.steiner_quadruple_system(32))
sage: time D.is_block_design()
CPU times: user 0.18 s, sys: 0.01 s, total: 0.19 s
Wall time: 0.17 s
(True, [2, 32, 4, 15])
}}}
--
Ticket URL: <http://trac.sagemath.org/ticket/15664>
Sage <http://www.sagemath.org>
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