#18624: Implement the lift theorem for linear matroids
-------------------------------------+-------------------------------------
Reporter: Rudi | Owner: Rudi
Type: enhancement | Status: needs_work
Priority: major | Milestone: sage-6.8
Component: matroid theory | Resolution:
Keywords: | Merged in:
Authors: Rudi Pendavingh | Reviewers: Michael Welsh
Report Upstream: N/A | Work issues:
Branch: | Commit:
u/Rudi/implement_the_lift_theorem_for_linear_matroids|
53903306acb3e9569d354284b1e8cbf1a3117119
Dependencies: | Stopgaps:
-------------------------------------+-------------------------------------
Changes (by yomcat):
* status: needs_review => needs_work
Comment:
Something isn't quite right:
{{{
sage: start_matrix = matrix(GF(19), [[18, 18, 18, 18, 18, 18, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 18, 0, 5], [1, 0, 0, 0, 0, 0, 18, 18, 18,
18, 18, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 15, 14], [0, 1, 0, 0, 0, 0, 1, 0,
0, 0, 0, 18, 18, 18, 18, 0, 0, 0, 0, 0, 0, 5, 4, 18], [0, 0, 1, 0, 0, 0,
0, 1, 0, 0, 0, 1, 0, 0, 0, 18, 18, 18, 0, 0, 0, 0, 0, 0], [0, 0, 0, 1, 0,
0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 1, 0, 0, 18, 18, 0, 14, 18, 0], [0, 0, 0, 0,
1, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 1, 0, 1, 0, 18, 0, 0, 0], [0, 0, 0, 0,
0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 1, 0, 1, 1, 1, 1, 1]])
sage: start_matrix
[18 18 18 18 18 18 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 18 0 5]
[ 1 0 0 0 0 0 18 18 18 18 18 0 0 0 0 0 0 0 0 0 0 0 15 14]
[ 0 1 0 0 0 0 1 0 0 0 0 18 18 18 18 0 0 0 0 0 0 5 4 18]
[ 0 0 1 0 0 0 0 1 0 0 0 1 0 0 0 18 18 18 0 0 0 0 0 0]
[ 0 0 0 1 0 0 0 0 1 0 0 0 1 0 0 1 0 0 18 18 0 14 18 0]
[ 0 0 0 0 1 0 0 0 0 1 0 0 0 1 0 0 1 0 1 0 18 0 0 0]
[ 0 0 0 0 0 1 0 0 0 0 1 0 0 0 1 0 0 1 0 1 1 1 1 1]
sage: GM = lift_map('gm')
sage: Z = lift_cross_ratios(start_matrix, GM)
---------------------------------------------------------------------------
ValueError Traceback (most recent call
last)
<ipython-input-11-d7b7e5f1514f> in <module>()
----> 1 Z = lift_cross_ratios(start_matrix, GM)
/Applications/sage-devel/local/lib/python2.7/site-
packages/sage/matroids/utilities.pyc in lift_cross_ratios(A, lift_map)
494
495 if cr != plus_one1 and not cr in lift_map:
--> 496 raise ValueError("Input matrix has a cross ratio
"+str(cr)+", which is not in the lift_map")
497 # - write the entry as a product of cross ratios of A
498 div = True
ValueError: Input matrix has a cross ratio 15, which is not in the
lift_map
sage: M = LinearMatroid(start_matrix)
sage: M.cross
M.cross_ratio M.cross_ratios
sage: M.cross_ratios()
{4, 5, 6, 14, 15, 16}
}}}
--
Ticket URL: <http://trac.sagemath.org/ticket/18624#comment:45>
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