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dormqr exact flop count?

Hello,

I would like to know the flop count of the function dormqr for some given parameters but I don't know where to find this information.

Likewise I would like to know the effective flop count for other functions such as dlarfp.

Can anyone advice?

TIA
Best regards,
Giovanni
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4 Replies
mecej4
Black Belt
42 Views

The flop count expressions ( expressions) for many linear algebra algorithms may be found in Matrix Computations by Golub and van Loan.

ISBN-13: 978-0801854149

yuriisig
Beginner
42 Views

dormqr from Intel MKL is a qualitative compilation of the source code dormqr (fortran, C) from package LAPACK. This package is accessible. dormqr has auxiliary value: where you use it?
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Hello mecej4,

I have the book and I know the theoretical complexities, however, the effective complexity of LAPACK functions that MKL provides is of course not there :) this is not really a simple matrix multiplication because it has to implicitly recover the Q first and apply it automagically to some matrix or vector. This is not covered in that book. Likewise the darfl type of functions that generate one column reflector to annihilate the non zero elements of a new column is not easy to find out unless you are a LAPACK Fortran guru.

It is impossible to know if e.g. some updates are improving the situation if I have no idea what flop count every MKL function I call has.

TIA,
Best regards,
Giovanni
yuriisig
Beginner
42 Views

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