Consider the following program that computes the spectrum and chromatic
number of a graph:
for g in graphs.nauty_geng(str(7)):
s = g.spectrum()
g.chromatic_number()
This works quickly and like a charm. Now consider the following program
that computes something related to the spectrum and chromatic number:
for g in graphs.nauty_geng(str(7)):
s = g.spectrum()
sp = sum([el**2 for el in s if el > 0])
sm = sum([el**2 for el in s if el < 0])
if sm != 0 and not (sp/sm+1 <= g.chromatic_number()):
print g.graph6_string()
The program gets stuck in computing something for a long time and in the
end it dies trying to allocate a ~7GB pari stack:
File "minw.py", line 9, in <module>
if sm != _sage_const_0 and not (sp/sm+_sage_const_1 <=
g.chromatic_number()):
File "element.pyx", line 902, in
sage.structure.element.Element.__richcmp__ (sage/structure/element.c:8480)
File "element.pyx", line 847, in sage.structure.element.Element._richcmp
(sage/structure/element.c:7930)
File "element.pyx", line 829, in sage.structure.element.Element._richcmp_
(sage/structure/element.c:7659)
File "element.pyx", line 874, in sage.structure.element.Element._richcmp
(sage/structure/element.c:8342)
File
"/home/azi/sage-5.3.rc1/local/lib/python2.7/site-packages/sage/rings/qqbar.py",
line 3755, in __cmp__
rcmp = cmp(self.real(), other.real())
File
"/home/azi/sage-5.3.rc1/local/lib/python2.7/site-packages/sage/rings/qqbar.py",
line 4395, in __cmp__
return self._sub_(other).sign()
File
"/home/azi/sage-5.3.rc1/local/lib/python2.7/site-packages/sage/rings/qqbar.py",
line 4611, in sign
return self.sign()
File
"/home/azi/sage-5.3.rc1/local/lib/python2.7/site-packages/sage/rings/qqbar.py",
line 4614, in sign
self.exactify()
File
"/home/azi/sage-5.3.rc1/local/lib/python2.7/site-packages/sage/rings/qqbar.py",
line 3466, in exactify
self._set_descr(self._descr.exactify())
File
"/home/azi/sage-5.3.rc1/local/lib/python2.7/site-packages/sage/rings/qqbar.py",
line 7591, in exactify
left.exactify()
File
"/home/azi/sage-5.3.rc1/local/lib/python2.7/site-packages/sage/rings/qqbar.py",
line 3466, in exactify
self._set_descr(self._descr.exactify())
File
"/home/azi/sage-5.3.rc1/local/lib/python2.7/site-packages/sage/rings/qqbar.py",
line 7334, in exactify
arg.exactify()
File
"/home/azi/sage-5.3.rc1/local/lib/python2.7/site-packages/sage/rings/qqbar.py",
line 3466, in exactify
self._set_descr(self._descr.exactify())
File
"/home/azi/sage-5.3.rc1/local/lib/python2.7/site-packages/sage/rings/qqbar.py",
line 7591, in exactify
left.exactify()
File
"/home/azi/sage-5.3.rc1/local/lib/python2.7/site-packages/sage/rings/qqbar.py",
line 3466, in exactify
self._set_descr(self._descr.exactify())
File
"/home/azi/sage-5.3.rc1/local/lib/python2.7/site-packages/sage/rings/qqbar.py",
line 7591, in exactify
left.exactify()
File
"/home/azi/sage-5.3.rc1/local/lib/python2.7/site-packages/sage/rings/qqbar.py",
line 3466, in exactify
self._set_descr(self._descr.exactify())
File
"/home/azi/sage-5.3.rc1/local/lib/python2.7/site-packages/sage/rings/qqbar.py",
line 7593, in exactify
gen = left._exact_field().union(right._exact_field())
File
"/home/azi/sage-5.3.rc1/local/lib/python2.7/site-packages/sage/rings/qqbar.py",
line 2276, in union
newpol, self_pol, k = pari_nf.rnfequation(my_factor, 1)
File "gen.pyx", line 10412, in sage.libs.pari.gen._pari_trap
(sage/libs/pari/gen.c:54794)
File "gen.pyx", line 9718, in sage.libs.pari.gen.PariInstance.allocatemem
(sage/libs/pari/gen.c:50859)
File "gen.pyx", line 10233, in sage.libs.pari.gen.init_stack
(sage/libs/pari/gen.c:53888)
MemoryError: Unable to allocate 65536000000 bytes memory for PARI.
What exactly is going on? From what I've checked into the sources I do not
see what is causing this issue? Am I doing something stupid in the second
sage program or is this some kind of Sage-Pari bug?
Best,
Jernej
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