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Multiplying sparse matrices

asked 2018-10-18 13:49:55 -0500

PW gravatar image

updated 2018-10-23 05:35:31 -0500

tmonteil gravatar image

Can Sage multiply sparse matrices? If so, does it require some special syntax? I've been trying to run the following code:

M = Matrix(QQ, 1000001, 1000001, {(3,2): 27, (2,98): 71})
M2 = M*M

and it hasn't been working. If M is being converted to a dense matrix for multiplication then of course I wouldn't expect this to run. But it shouldn't be hard to do as sparse matrices, right?

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answered 2018-10-18 14:13:44 -0500

nbruin gravatar image

I think the relevant code is here:

The algorithm does take into account the sparse nature, but it does have a triple-nested for-loop, enumerating all the indices. It may be that for moderate sparsity this is faster than just enumerating the non-zero entries, but especially for your example it's pretty clear a much more efficient implementation is possible.

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answered 2018-10-23 05:35:12 -0500

tmonteil gravatar image

Thanks for reporting, this is now trac ticket 26532.

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Asked: 2018-10-18 13:49:55 -0500

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Last updated: Oct 23 '18