#20470: Conversion of sparse to dense matrices over F2 is unspeakably slow
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Reporter: kedlaya | Owner:
Type: defect | Status: new
Priority: major | Milestone: sage-7.2
Component: linear algebra | Resolution:
Keywords: sparse matrices, dense | Merged in:
matrices | Reviewers:
Authors: | Work issues:
Report Upstream: N/A | Commit:
Branch: | Stopgaps:
Dependencies: |
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Comment (by kedlaya):
Replying to [comment:1 jhpalmieri]:
> How much time does
> {{{
> time sT2F2a = sT2F2.dense_matrix()
> }}}
> take? I tried with a smaller matrix, and it's much faster than plugging
the matrix into the appropriate matrix space. (That doesn't mean that
there isn't a problem, rather that someone could possibly speed up `M2(
sparse_matrix )` by calling the `dense_matrix()` method, under suitable
circumstances.)
That is indeed much faster:
{{{
sage: time sT2F2b = sT2F2.dense_matrix()
CPU times: user 318 ms, sys: 47 ms, total: 365 ms
Wall time: 365 ms
sage: sT2F2a == sT2F2b
True
}}}
I guess that means this is easy to fix: the constructor for dense matrices
(over any base), upon receiving a sparse matrix as input, should simply
call the `dense_matrix()` method.
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Ticket URL: <http://trac.sagemath.org/ticket/20470#comment:2>
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