On Fri, Jun 1, 2012 at 10:59 AM, Jeroen Demeyer <jdeme...@cage.ugent.be> wrote:
> Looks like an infinite recursion, leading to stack exhaustion, leading
> to a SIGSEGV:
I agree with the last two but not the first. I think it's just a
really long LazyBinop chain, which is why I was having trouble
debugging the problematic part of polynomial_element.pyx:
elif (d < 4 or d > 50000) and self._compiled is None:
while i >= 0:
result = result * a + self[i]
i -= 1
Even putting in print statements triggered "unlazification", or
whatever the word is (evaluation?), which blew the stack. For
example:
-----
from sage.rings.real_lazy import LazyBinop
def loop(n):
x = RealLazyField()(1)
for i in xrange(n):
x = LazyBinop(RLF, x, x, operator.mul)
-----
produces
sage: loop(10)
sage: loop(100)
sage: loop(1000)
sage: loop(10000)
sage: loop(100000)
sage: loop(1000000)
/home/mcneil/sagedev/sage-5.1.beta1/spkg/bin/sage: line 326: 8729
Segmentation fault (core dumped) sage-ipython "$@" -i
Doug
PS:
Side issue #1: evaluating LazyBinops is *really* slow as soon as
there get to be more than a few terms.
Side issue # 2: it looks weird to me that we loop over every item in
the polynomial list rather than over every coefficient in the elif
branch I quoted above. Having lots of zeroes is a pretty common use
case, I'd've thought.
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