# Matrix multiplication not returning on certain matrix content (Intel)

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Hi,

I have a certain matrix multiplication which is not returning on my Intel machine (Win11 Pro, Intel i7-8700). When I exchange the content of the matrices with random numbers I can obtain a result within seconds. I could reproduce this problem on several Intel machines (and different Matlab versions). I relate this problem to Intel MKL. One matrix contains a lot of entries close to zero (10^-322) which probably causes the problem.

To reproduce it, download the two matrices:

and run the command:

scc=At*scc;

Is this operation running through on your machine?

##### 2 Comments

John D'Errico
on 10 Apr 2024

It is generally a bad idea to force someone to download a file from off-site. We don't know if you are planting a trojan on our system. Honestly, I won't touch it to test your question as a download. Maybe others will be more willing to take a chance on an unknown person, posting a link to an unkown file. I hope they don't take the risk since you could have made this much simpler.

Just attach a .mat file that contains the matrices. Click on the paper clip icon on a comment.

### Answers (1)

Bruno Luong
on 10 Apr 2024

Edited: Bruno Luong
on 10 Apr 2024

The matrix contains many non normalized floating point numbers and operations on these numbers are very slow;

>> load('C:\Users\bruno\Downloads\test.mat')

>> size(At)

ans =

17534 17532

>> size(scc)

ans =

17532 8281

>> tic; B=At*scc(:,1); toc

Elapsed time is 1.105924 seconds.

>> tic; B=At*scc(:,1:10); toc

Elapsed time is 10.237435 seconds.

>> tic; B=At*scc(:,1:100); toc

Elapsed time is 108.484422 seconds.

On my machine it takes 1 sec by column of scc. So eventually I guess it will finish in less than 3h.

Note that for normalized numbers the operation is roughly 200 time faster.

So for now I think there is no bug. Just let the thing run over night (Sorry I won't do that).

##### 13 Comments

Walter Roberson
on 11 Apr 2024

Bruno Luong
on 11 Apr 2024

Edited: Bruno Luong
on 11 Apr 2024

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