From plummer at iarc.fr  Wed Nov  5 22:02:02 2008
From: plummer at iarc.fr (plummer at iarc.fr)
Date: Wed, 05 Nov 2008 22:02:02 +0100
Subject: [Rd] [R] Building with MKL on Ubuntu
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Message-ID: <1225918922.491209ca64fd5@webmail.iarc.fr>

Quoting Peter Dalgaard <P.Dalgaard at biostat.ku.dk>:

> Anand Patil wrote:
> > On Wed, Nov 5, 2008 at 5:59 PM, Martyn Plummer <plummer at iarc.fr> wrote:
> >
> >> It looks like the em64t version of MKL fails the test for the accuracy
> >> of zdotu ("checking whether double complex BLAS can be used") and is
> >> therefore dropped in favour of R's built-in BLAS.  I have just tested
> >> this on Fedora and get the same result.
> >>
> >> The 32-bit MKL does work for me.
> >>
> >> Martyn
> >>
> >
> > Many thanks, Martyn. The 64-bit index space is important to me, will I lose
> > it if I link against the 32-bit MKL? Also, should I file a bug report with
> > Intel?
> > Anand
>
> There's also the option of "breaking the thermometer". You might examine
> that check and decide whether the loss of accuracy is enough for you to
> worry about and if not, take out the test from configure.
>
> Apparently, this check was put in place in R-2.2.0
>
>     o Any external BLAS found is now tested to see if the complex
>         routine zdotu works correctly: this provides a compatibility
>         test of compiler return conventions.
>
> which suggests that the expected failure is catastrophic, and looking at
> the code, there's a fuzz of 1e-10 which would seem to be about 1e5 times
> larger than required.

My apologies. I skimmed the code of the test program, but as Brian says
it is not a question of accuracy. The test program does in fact segfault,
although you won't see this in your config.log.

Anyway, Anand, I would just carry on with libRblas.

Martyn



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[Rd] [R] Building with MKL on Ubuntu
plummer at iarc.fr