#4533: [with patch; needs work] divisors function slow for integers
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Reporter: robertwb | Owner: tbd
Type: defect | Status: new
Priority: major | Milestone: sage-3.2.1
Component: algebra | Resolution:
Keywords: |
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Comment (by robertwb):
I'll make those fixes, and write a special case for word-sized integers.
It should be noted that *sorting* the output often takes the majority of
the time
{{{
sage: sage: n = ZZ(odd_part(factorial(31)))
sage: sage: time _ = divisors(n)
CPU times: user 0.53 s, sys: 0.02 s, total: 0.54 s
Wall time: 0.55 s
sage: sage: time _ = divisors(n, sorted=False)
CPU times: user 0.15 s, sys: 0.02 s, total: 0.17 s
Wall time: 0.17 s
sage: n = factorial(25)
sage: time _ = divisors(n)
CPU times: user 1.07 s, sys: 0.05 s, total: 1.12 s
Wall time: 1.12 s
sage: time _ = divisors(n, sorted=False)
CPU times: user 0.33 s, sys: 0.05 s, total: 0.38 s
Wall time: 0.38 s
}}}
Originally I wasn't sorting the output, which was why I thought I was so
much faster. (The original code sorted the output too, but it was slow
enough that the sorting didn't dominate.)
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/4533#comment:8>
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