#7492: Decomposition of a doubly stochastic matrix as a convex sum of
permutations
(Birkhoff–von Neumann Theorem)
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Reporter: ncohen | Owner: mhansen
Type: enhancement | Status: needs_work
Priority: major | Milestone: sage-4.4.2
Component: combinatorics | Keywords:
Author: Nathann Cohen | Upstream: N/A
Reviewer: Mike Hansen | Merged:
Work_issues: |
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Changes (by davidloeffler):
* status: needs_review => needs_work
Comment:
Needs work, I'm afraid.
- Firstly, there are no checks on the input type. It will happily accept
non-doubly-stochastic matrices, and return garbage; and it seems to
silently replace real numbers with rational approximations to them, which
is frankly rather weird. The docstring should state clearly what base
rings are allowed (integers? rationals? reals?) and there should be a
check to make sure that the input matrix really is a doubly stochastic
matrix over one of these base rings.
- The doctests won't work without an optional spkg, so they should be
flagged as such.
- Non-ASCII character in the docstring (it reads as "Birkhoff[a-with-
circumflex][empty-square-box][empty-square-box]von Neumann" on my system)
- There's not a lot of point in adding functions when there's no obvious
way of calling them from the command line. Either this should be imported
in an all.py somewhere, or (much preferably) there should be a method of
one of the matrix classes that calls it.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/7492#comment:7>
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