#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: positive_review
Priority: major | Milestone: sage-5.0
Component: linear algebra | Keywords: rd2
Work_issues: | Upstream: N/A
Reviewer: Rob Beezer | Author: Punarbasu Purkayastha
Merged: | Dependencies:
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Changes (by newvalueoldvalue):
* keywords: => rd2
* reviewer: => Rob Beezer
* status: needs_review => positive_review
* author: => Punarbasu Purkayastha
Old description:
> The implementation of the density method for a sparse matrix is insane.
> It loops through every single index possible and asks if each entry is
> zero or nonzero:
>
> {{{
> sage: A=matrix(5000,5000,{(1,2): 1})
> sage: A.density()
> 1/25000000
> }}}
>
> An implementation that instead relied on `A.nonzero_positions()` would be
> orders of magnitude faster.
New description:
The implementation of the density method for a sparse matrix is insane.
It loops through every single index possible and asks if each entry is
zero or nonzero:
{{{
sage: A=matrix(5000,5000,{(1,2): 1})
sage: A.density()
1/25000000
}}}
An implementation that instead relied on `A.nonzero_positions()` would be
orders of magnitude faster.
'''Apply:'''
1. [attachment:trac_12499-faster-sparse-matrix-density.patch]
--
Comment:
Looks good. Positive review.
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Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/12499#comment:8>
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