#12499: The density() function of a sparse matrix looks at every matrix entry
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Reporter: jason | Owner: jason, was
Type: defect | Status: needs_review
Priority: major | Milestone: sage-5.0
Component: linear algebra | Keywords:
Work_issues: | Upstream: N/A
Reviewer: | Author:
Merged: | Dependencies:
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Comment(by dsm):
I think we can improve this further, especially for denser matrices, by
adding copy=False:
{{{
sage: A = MatrixSpace(ZZ, 5000,sparse=True).random_element(density=0.02)
sage: A
5000 x 5000 sparse matrix over Integer Ring (type 'print A.str()' to see
all of the entries)
sage: %timeit QQ(len(A.nonzero_positions()))/(QQ(A.nrows()*A.ncols()))
25 loops, best of 3: 16.5 ms per loop
sage: %timeit
QQ(len(A.nonzero_positions(copy=False)))/QQ(A.nrows()*A.ncols())
625 loops, best of 3: 14.3 µs per loop
sage: %timeit
QQ(len(A.nonzero_positions(copy=False)))/(A.nrows()*A.ncols())
625 loops, best of 3: 13.3 µs per loop
}}}
Removing the second QQ is a micro-optimization but buys you a little..
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Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/12499#comment:2>
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