[R] Understanding dsyrk_ in C code

[Nathan S. Watson-Haigh]

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I'm trying to understand some C code in an R package I'm using. I'm address this question here as
it's matrix algebra...and I'm no pro at that!

the C command reads:

double alpha = 1.0, beta = 0.0;
dsyrk_("L", "N", nGenes, nGenes, & alpha, mat1, nGenes,
         & beta, mat2, nGenes);

- From google, I've found out that dsyrk is for performing one of the symmetric rank k operations -
whatever that means!? From here:
http://linux.die.net/man/l/dsyrk

I've found that the calculation being performed is:
alpha*A*A' + beta*C

However, since alpha is 1 and beta is 0, this reduces to:
=> 1*A*A' + 0*C
=> A*A'

Which is simply the cross product....am I correct?

Cheers,
Nath

- --
- --------------------------------------------------------
Dr. Nathan S. Watson-Haigh
OCE Post Doctoral Fellow
CSIRO Livestock Industries
Queensland Bioscience Precinct
St Lucia, QLD 4067
Australia

Tel: +61 (0)7 3214 2922
Fax: +61 (0)7 3214 2900
Web: http://www.csiro.au/people/Nathan.Watson-Haigh.html
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