#3436: random_matrix() with prescribed density buggy
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Reporter: rpw | Owner: was
Type: defect | Status: needs_review
Priority: major | Milestone: sage-4.3.1
Component: linear algebra | Keywords:
Author: spancratz | Upstream: N/A
Reviewer: | Merged:
Work_issues: |
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Comment(by spancratz):
Here are the timings for the code that Tom wrote, which gets rid of the
"ugly" code I wrote for generating the random matrices over cyclotomic
fields and instead uses the generic code of random elements in cyclotomic
fields (implemented by two of the patches above):
{{{
sage: MS = MatrixSpace(CyclotomicField(10), 100, 100)
sage: time A = MS.random_element()
CPU times: user 27.11 s, sys: 0.35 s, total: 27.46 s
Wall time: 27.46 s
}}}
I suspect that the slowness of this code is largely due to the fact that
for every random element of the cyclotomic field, two conversions take
place. One of a random list of rationals into the polynomial ring, and
then another of that polynomial into the polynomial quotient ring.
I don't think there is much we can do about this at the moment. Thus, I
propose that we should apply all of the patches on this ticket apart from
``trac3436-tb.patch``. I'll flatten them a little, (1) main patch (2)
``random_element`` in polynomial rings, polynomial quotient rings, and
number fields. Hopefully, this will then pass all doctests and we'll be
done.
Any comments?
PS: Of course, I'll include the fixed doctests (64-bit difference) from
Tom's patch.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/3436#comment:21>
Sage <http://www.sagemath.org>
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