[Rd] Thought on crossprod
Fri, 15 Mar 2002 17:13:31 +0000 (GMT)
On Fri, 15 Mar 2002, Thomas Lumley wrote:
> On Fri, 15 Mar 2002, Martin Maechler wrote:
> > >>>>> "JonR" == Jonathan Rougier <J.C.Rougier@durham.ac.uk> writes:
> > JonR> does not recognise the case where y is the same as x as special. I'd
> > JonR> like to extend crossprod to something like
> > >> crossprod
> > JonR> function(x, y = NULL)
> > JonR> if (is.null(y))
> > JonR> .Internal(crossprod.symm(x))
> > JonR> else
> > JonR> .Internal(crossprod(x, y))
> > JonR> Before I start mesing up my R-1.4.1 installation, does anyone have any
> > JonR> thoughts on this?
> > Just for clarification:
> > The main point of your suggestion is to pass only half as much
> > data down to C, right?
> If this can be done with the BLAS functions then halving the necessary
> memory bandwidth will also help -- that's one of the limiting factors in
> ATLAS, for example.
Looks like dsyrk can do this: despite the definition of *sy* BLAS routines
on my quick reference card it does not need a symmetric matrix, which is
why I overlooked it in earlier correspondence with Jonathan. As from
1.5.0 dsyrk will be available in R.
Brian D. Ripley, firstname.lastname@example.org
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 272860 (secr)
Oxford OX1 3TG, UK Fax: +44 1865 272595
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