R help - Feb 2006 - How can I see how %*% is implemented?

I would like to see how the matrix multiplication operator %*% is implemented
(because I want to see which external Fortran/C routines are used). How can I do
so?
Best
S??ren

On Wed, 22 Feb 2006, S??ren H??jsgaard wrote:
> I would like to see how the matrix multiplication operator %*% is 
> implemented (because I want to see which external Fortran/C routines are 
> used). How can I do so? Best S??ren
[This is probably a R-devel question: please study the posting guide.]
> get("%*%")
.Primitive("%*%")

so get your R sources out (I'll use current R-devel), go to 
src/main/names.c and search.  You find

{"%*%",         do_matprod,     0,      1,      2,      {PP_BINARY, 
PREC_PERCENT,0}},

So this is OP 0 of do_matprod.  Search for that in src/main/*.c: it is is 
array.c. Find

     if (PRIMVAL(op) == 0) {			/* op == 0 : matprod() */

and the meat is

 	if (mode == CPLXSXP)
 	    cmatprod(COMPLEX(CAR(args)), nrx, ncx,
 		     COMPLEX(CADR(args)), nry, ncy, COMPLEX(ans));
 	else
 	    matprod(REAL(CAR(args)), nrx, ncx,
 		    REAL(CADR(args)), nry, ncy, REAL(ans));

Now look for matprod and cmatprod.  The answer is that if there are no 
IEEE754 specials, dgemm or zgemm are used.  Those are level-3 BLAS 
routines.

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

get("%*%")

tells you that it is a primitive (i.e., implemented in C). The file
<R_HOME>/src/main/names.c directs you to do_matprod, in file
<R_HOME/src/main/array.c.

Martin

S??ren H??jsgaard <Soren.Hojsgaard at agrsci.dk> writes:
> I would like to see how the matrix multiplication operator %*% is
implemented (because I want to see which external Fortran/C routines are used).
How can I do so?
> Best
> S??ren
>
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