#17640: Error in function Graph.odd_girth()
----------------------------+-----------------------
Reporter: ffoucaud | Owner:
Type: defect | Status: new
Priority: major | Milestone:
Component: graph theory | Keywords:
Merged in: | Authors:
Reviewers: | Report Upstream: N/A
Work issues: | Branch:
Commit: | Dependencies:
Stopgaps: |
----------------------------+-----------------------
Hi,
I'm doing some computations based on enumerating graphs via
"nauty_geng()". There, I test the odd girth of the generated graphs, and
after several hours of graph enumeration, the computations stop ith
errors. The errors seem to come from the function "odd_girth()" associated
to the "Graph" class, with, according to the error message, a possible
relation with matrices and primes (see below).
Note: I realise that I am using the precompiled version 5.8 of sage that
comes with the ubuntu repository (ubuntu 12.04). So maybe this is fixed in
newer versions... In any case I will now use the latest release.
Here is my code:
{{{
def OG7_NOhomC5(begin,end):
F=[]
C5=graphs.CycleGraph(5)
for n in [begin .. end]: #range for orders
for g in graphs.nauty_geng("%s -c -t -d2 -D6"%n):
if g.girth()==4 and g.odd_girth()>=7:
maps=g.has_homomorphism_to(C5)
if maps == False:
F += [(g.graph6_string())]
print ' found :-)',F
OG7_NOhomC5(14,14)
}}}
And here are 2 different tracebacks, both with an error located in
"odd_girth()":
{{{
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "_sage_input_3.py", line 10, in <module>
exec compile(u'open("___code___.py","w").write("# -*- coding: utf-8
-*-\\n" +
_support_.preparse_worksheet_cell(base64.b64decode("T0c3X05PaG9tQzUoMTQsMTQp"),globals())+"\\n");
execfile(os.path.abspath("___code___.py"))
File "", line 1, in <module>
File "/tmp/tmpPMZ4j_/___code___.py", line 3, in <module>
exec compile(u'OG7_NOhomC5(_sage_const_14 ,_sage_const_14 )
File "", line 1, in <module>
File "/tmp/tmp1XHck_/___code___.py", line 10, in OG7_NOhomC5
if g.girth()==_sage_const_4 and g.odd_girth()>=_sage_const_7 :
File "/usr/lib/sagemath/local/lib/python2.7/site-
packages/sage/graphs/graph.py", line 2388, in odd_girth
ch = ((self.am()).charpoly()).coeffs()
File "matrix_integer_dense.pyx", line 1042, in
sage.matrix.matrix_integer_dense.Matrix_integer_dense.charpoly
(sage/matrix/matrix_integer_dense.c:11571)
File "matrix_integer_dense.pyx", line 1099, in
sage.matrix.matrix_integer_dense.Matrix_integer_dense._charpoly_linbox
(sage/matrix/matrix_integer_dense.c:12253)
File "matrix_integer_dense.pyx", line 1121, in
sage.matrix.matrix_integer_dense.Matrix_integer_dense._poly_linbox
(sage/matrix/matrix_integer_dense.c:12534)
RuntimeError: Segmentation fault
}}}
{{{
you are running out of primes. 1000 coprime primes foundTraceback (most
recent call last):
File "<stdin>", line 1, in <module>
File "_sage_input_4.py", line 10, in <module>
exec compile(u'open("___code___.py","w").write("# -*- coding: utf-8
-*-\\n" +
_support_.preparse_worksheet_cell(base64.b64decode("T0c3X05PaG9tQzUoMTMsMTMp"),globals())+"\\n");
execfile(os.path.abspath("___code___.py"))
File "", line 1, in <module>
File "/tmp/tmpRfy2qw/___code___.py", line 3, in <module>
exec compile(u'OG7_NOhomC5(_sage_const_13 ,_sage_const_13 )
File "", line 1, in <module>
File "/tmp/tmp1inrim/___code___.py", line 10, in OG7_NOhomC5
if g.girth()==_sage_const_4 and g.odd_girth()>=_sage_const_7 :
File "/usr/lib/sagemath/local/lib/python2.7/site-
packages/sage/graphs/graph.py", line 2392, in odd_girth
if ch[i] != 0:
IndexError: list index out of range
}}}
--
Ticket URL: <http://trac.sagemath.org/ticket/17640>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
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