#12901: permutation_automorphism_group fails in optional doctest of
coding/linear_code.py
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Reporter: benjaminfjones | Owner: wdj
Type: defect | Status: new
Priority: minor | Milestone: sage-5.1
Component: coding theory | Resolution:
Keywords: linear code gap | Work issues:
Report Upstream: N/A | Reviewers:
Authors: | Merged in:
Dependencies: | Stopgaps:
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Comment (by benjaminfjones):
From my initial investigation is seems that the failure occurs when the
GAP function `MatrixAutomorphisms` is called with an empty matrix `[ ]` as
it's argument.
An example where the problem occurs,
{{{
sage: C = HammingCode(2,GF(4,"z")); C
Linear code of length 5, dimension 3 over Finite Field in z of size 2^2
sage: C.permutation_automorphism_group(algorithm="partition")
Permutation Group with generators [(1,3)(4,5), (1,4)(3,5)]
sage: C.permutation_automorphism_group(algorithm="gap")
...
TypeError: Gap produced error output
Error, no 1st choice method found for `MatrixAutomorphisms' on 1 arguments
executing $sage26:=MatrixAutomorphisms(matCwt);;
}}}
When I trace `C.permutation_automorphism_group(algorithm="gap")` in this
example, I see that
{{{
1922 gap.eval("matCwt:=List(Cwt,c->VectorCodeword(c))")
# for each i until stop = 1)
-> 1923 A = gap("MatrixAutomorphisms(matCwt)")
1924 #print "A = ",A, "\n Gp = ", Gp, "\n strGp = ",
str(Gp)
ipdb> print wt
3
ipdb> print nonzerowts
[0, 3, 4, 5]
ipdb> gap("Cwt")
[ ]
ipdb> gap("List(eltsC, c->WeightCodeword(c))")
[ 0, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4 ]
}}}
so it looks to me like we're expecting to find vectors of weight 3, 4, and
5, but according to GAP there are only vectors of weight 0 or 4 in the
code.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/12901#comment:1>
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