BLAS DGEMM: Can I pass C as A or B?

Question

I want to perform a string of matrix multiplies, and would prefer not allocate a fresh matrix if I can avoid it. For example, I want to compute C = C * B (so I pass in C as A and C)

Can I do this (due to dgemm having marked both A and B as in variables)?

score 3 · Answer 1 · answered Dec 12 '12 at 07:32

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None of the BLAS implementations I have even used had a dgemm which could work in-place.

answered Dec 12 '12 at 07:32

talonmies

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score 3 · Accepted Answer · edited May 23 '17 at 10:24

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No, you can never do this and it has nothing to do with the BLAS implementation. See

Is it safe to pass GEMV the same output- as input vector to achieve a destructive matrix application?

edited May 23 '17 at 10:24

Community

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answered Dec 12 '12 at 08:12

Ian Bush

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BLAS DGEMM: Can I pass C as A or B?

2 Answers2