From tlumley@u.washington.edu  Fri Mar 15 16:42:58 2002
From: tlumley@u.washington.edu (Thomas Lumley)
Date: Fri, 15 Mar 2002 08:42:58 -0800 (PST)
Subject: [Rd] Thought on crossprod
In-Reply-To: <15505.64244.865792.272476@gargle.gargle.HOWL>
Message-ID: <Pine.A41.4.44.0203150840250.25112-100000@homer14.u.washington.edu>

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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[Rd] Thought on crossprod
Thomas Lumley