[Rd] Fixed BLAS tests for external BLAS library

Tomas Kalibera tomas.kalibera at gmail.com
Fri Jan 5 00:41:47 CET 2018

In practical terms, failing tests are not preventing anyone from using 
an optimized BLAS/LAPACK implementation they trust. Building R with 
dynamically linked BLAS on Unix is supported, documented and easy for 
anyone who builds R from source. It is also how Debian/Ubuntu R packages 
are built by default, so R uses whichever BLAS is installed in the 
system and the user does not have to build from source. There is no 
reason why not to do the same thing with another optimized BLAS on 
another OS/distribution.

You may be right that reg-BLAS is too strict (it is testing matrix 
products, expecting equivalence to naive three-loop algorithm, just part 
of it really uses BLAS). I just wanted a concrete example to think about 
as I can't repeat it (e.g. it passes with openblas), but maybe someone 
else will be able to repeat and possibly adjust.


On 01/04/2018 09:23 PM, Simon Guest wrote:
> Hi Tomas,
> Thanks for your reply.
> I find your response curious, however.  Surely the identical() test is 
> simply incorrect when catering for possibly different BLAS 
> implementations?  Or is it the case that conformant BLAS 
> implementations all produce bit-identical results, which seems 
> unlikely?  (Sorry, I am unfamiliar with the BLAS spec.)  Although 
> whatever the answer to this theoretical question, the CentOS 7 
> external BLAS library evidently doesn't produce bit-identical results.
> If you don't agree that replacing identical() with all.equal() is 
> clearly the right thing to do, as demonstrated by the CentOS 7 
> external BLAS library failing the test, then I think I will give up 
> now trying to help improve the R sources.  I simply can't justify to 
> my client more time spent on making this work, when we already have a 
> local solution (which I hoped others would be able to benefit from).  
> Ah well.
> cheers,
> Simon
> On 5 January 2018 at 00:07, Tomas Kalibera <tomas.kalibera at gmail.com 
> <mailto:tomas.kalibera at gmail.com>> wrote:
>     Hi Simon,
>     we'd need more information to consider this - particularly which
>     expression gives an imprecise result with ACML and what are the
>     computed values, differences. It is not common for optimized BLAS
>     implementations to fail reg-BLAS.R tests, but it is common for
>     them to report numerical differences in tests of various
>     recommended packages where more complicated computations are done
>     (e.g. nlme), on various platforms.
>     Best
>     Tomas
>     On 12/18/2017 08:56 PM, Simon Guest wrote:
>         We build R with dynamically linked BLAS and LAPACK libraries,
>         in order
>         to use the AMD Core Math Library (ACML) multi-threaded
>         implementation
>         of these routines on our 64 core servers.  This is great, and our
>         users really appreciate it.
>         However, when building like this, make check fails on the
>         reg-BLAS.R
>         test.  The reason for this is that the expected test output is
>         checked
>         using identical.  By changing all uses of identical in this
>         file to
>         all.equal, the tests pass.
>         Specifically, I run this command before make check:
>         $ sed -i -e 's/identical/all.equal/g' tests/reg-BLAS.R
>         I suggest that the test is fixed like this in the R source code.
>         Here is the configure command I use, on CentOS 7:
>         $ ./configure --with-system-zlib --with-system-bzlib
>         --with-system-pcre \
>              --with-blas \
>              --with-lapack \
>              --with-tcl-config=/usr/lib64/tclConfig.sh \
>              --with-tk-config=/usr/lib64/tkConfig.sh \
>              --enable-R-shlib \
>              --enable-prebuilt-html
>         cheers,
>         Simon
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