#13196: GL(n, GF(q)).random_element() is way too slow for what it does
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Reporter: Bouillaguet | Owner:
joyner
Type: enhancement | Status:
needs_work
Priority: trivial | Milestone:
sage-5.2
Component: group theory | Resolution:
Keywords: matrix group, finite field, random element | Work issues:
Report Upstream: N/A | Reviewers:
Authors: Charles Bouillaguet | Merged in:
Dependencies: | Stopgaps:
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Comment (by dimpase):
Replying to [comment:5 Bouillaguet]:
> Replying to [comment:4 dimpase]:
> > Could you add in the docstring that the probaility to get an
invertible element is about 1/3, and so we expect to get the
> > answer in about 3 iterations ?
>
> This is not true. The expected number of iterations is asymptotically `1
+ 1/q + 2/q^2 + 3/q^3 + 5/q^4 + 7/q^5 + ....`
>
> For `GF(2)` you have 3.5 expected iterations, but for GF(127) you have
1.008 iterations..... So that asymptotically, the number of iterations is
O(1), and the complexity of the procedure is `O(n^3)`, regardless of the
size of the field.
>
> Is that OK with you ?
sure. I meant to say "at most 3 iterations".
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Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/13196#comment:6>
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