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Re: Dot product full-sparse


From: Jaroslav Hajek
Subject: Re: Dot product full-sparse
Date: Thu, 12 Aug 2010 09:04:56 +0200

On Wed, Aug 11, 2010 at 8:20 AM, Marco Caliari <address@hidden> wrote:
> Dear maintainers,
>
> if I run
>
> A = toeplitz ([-2, 1, 1, 1, zeros(1, 856)]);
> A = reshape (A, 18490, 40);
> SA = sparse (A);
> B = rand (size (A));
> tic, A .* B;,toc
> tic, SA .* B;, toc
> tic, SA .* sparse (B);, toc
>
> I get
>
> Elapsed time is 0.00745105 seconds.
> Elapsed time is 0.229055 seconds.
> Elapsed time is 0.0203849 seconds.
>
> (3.3.51 with Suitesparse 3.5.0, similar results with 3.2.4 with Suitesparse
> 3.4.0). Why SA .* sparse (B) is so faster than SA .* B? What is done by
> default when a full-sparse dot product is required?
>
> Best regards,
>
> Marco
>

Apparently this operation is just poorly optimized.

Before I start doing anything here, I'd like to know what the Matlab
behavior is w.r.t. NaNs. Namely, if
A = sparse ([2,3,1,2], [1,1,3,3], [0.1, 0.2, 0.3, 0.4]);
B = ones (3); B(1,1) = NaN;
C = sparse ([1,2,3,1,2], [1,1,1,3,3], [NaN, 0.1, 0.2, 0.3, 0.4]);

what is the output of A.*B, B.*A, A ./ B, A .*C?
Of course, newer version is better.

regards

-- 
RNDr. Jaroslav Hajek, PhD
computing expert & GNU Octave developer
Aeronautical Research and Test Institute (VZLU)
Prague, Czech Republic
url: www.highegg.matfyz.cz


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