#13413: fix integer overflow (?) in conversion of powersums to Schur functions
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Reporter: saliola | Owner: sage-combinat
Type: defect | Status: new
Priority: major | Milestone: sage-5.4
Component: combinatorics | Resolution:
Keywords: symmetric functions | Work issues:
Report Upstream: N/A | Reviewers:
Authors: | Merged in:
Dependencies: | Stopgaps:
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Changes (by mguaypaq):
* cc: mguaypaq (added)
Comment:
Running the attached file {{{symmetrica-test.py}}} exhibits the problem on
some machines (e.g., a Mac of some sort, I don't have the specs with me)
but on my own laptop (ancient Dell laptop running Ubuntu 10.04 LTS) the
test runs out of memory before finding a problem. Curiously enough, for
the Mac I tried the problem appears at size 47, same as in the problem
description.
I think this shows that the problem is in (or extremely close to)
Symmetrica, not Sage itself.
Also, given that the coefficients change even without any intervening
computations, I strongly suspect that we're seeing a memory leak in
Symmetrica, not an integer overflow error. Most likely,
1. Symmetrica computes some result,
1. caches a pointer to the result,
1. frees the memory containing the result,
1. this memory eventually gets reused,
1. so the cached result now points to garbage.
It's interesting to note that the error only seems to happen when dealing
with coefficients in {{{QQ}}}, not in {{{ZZ}}}, as Anne's testing shows.
However, given the state of the Symmetrica source code, I'm not optimistic
about actually finding (and fixing) the bug.
Do we know if there are other changes of basis which exhibit similar
problems?
For convenience, note that the content of {{{symmetrica-test.py}}} is
simply:
{{{
from sage.all import QQ, ZZ, Partition
from sage.libs.symmetrica.all import t_POWSYM_SCHUR as convert
from time import time
one = QQ(1)
bad_input = {Partition([ZZ(2)] * 2): one}
good_output = convert(bad_input)
start_time = time()
k = 1
while True:
dummy = convert({Partition([ZZ(1)] * k): one})
if convert(bad_input) != good_output: break
print 'Size %d seems fine after %d seconds.' % (k, time() -
start_time)
k += 1
print 'Found a problem at size %d:' % k
for k in range(10):
print convert(bad_input)
}}}
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/13413#comment:3>
Sage <http://www.sagemath.org>
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