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https://issues.apache.org/jira/browse/MATH-248?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12675698#action_12675698
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Christian Semrau commented on MATH-248:
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According to my little tests, walking in optimized order and adding the
pairwise products to the result matrix is much faster for very sparse matrices,
but for a full matrix (every entry set to 1), it is about 50% slower than the
current implementation. So the implementation might switch between the two
algorithms. Also one might wish to walk the other matrix if it is more sparse
than this.
> Multiplying sparse matrices is slow
> -----------------------------------
>
> Key: MATH-248
> URL: https://issues.apache.org/jira/browse/MATH-248
> Project: Commons Math
> Issue Type: Improvement
> Reporter: Christian Semrau
> Priority: Minor
>
> The multiplication of sparse real matrices is very slow compared to real
> matrices: Ten times as slow for size 200, four times as slow for size 400.
> The time is independent of the number of nonzero entries, because the general
> algorithm inherited from AbstractRealMatrix is used. I suggest using a
> specialized multiplication algorithm for matrices that are "sparse enough",
> walking only over the nonzero entries in one of the matrices.
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