[Rd] Thought on crossprod

[Thomas Lumley]

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.

	-thomas

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