On Wed, 7 Jan 2009, Nathan S. Watson-Haigh wrote:
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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);
That's a Fortran subroutine. The code is in blas.f (as 'DSYRK') and is
commented. So, you should be able to work thru it.
If you want to see how it is used, grep the sources for 'dsyrk' (lower
case). I think array.c uses it for symmetric crossproducts along the lines
of the alpha=1.0 and beta = 0.0 example you cite.
It is often a good idea to search the R sources for routines whose
function is puzzling and find examples of their use to help one understand
what they do.
HTH,
Chuck
- 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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