[Pw_forum] How to convince QE from local lapack/blas?

[Guntram Schmidt]

Dear Paolo!

Thanks a lot for this clearification! It finally got me to be able to 
use essl, though.
I had to use -D__ESSL instead of D_LINUX_ESSL (suggested by ./configure)!

Finally a last question: Is is meaningfull to have the internal lapack 
loaded after the external one?

I mean:

LAPACK_LIBS    =  -lessl -L/gpfs/usrurz/lib64 -llapack 
/gpfs/home/aasfu/espresso-4.3.2/lapack-3.2/lapack.a

vs.

LAPACK_LIBS    =  -lessl -L/gpfs/usrurz/lib64 -llapack

/gpfs/usrurz/lib64/liblapack.a beeing our local compiled version.

Thank you,
Guntram



Am 27.07.2011 22:31, schrieb Paolo Giannozzi:
>
> On Jul 27, 2011, at 5:40 , Michael Sullivan wrote:
>
>> If I'm not wrong, that just means that you're not using ESSL.
>
> it is true that by linking lapack before essl, the lapack version
> of lapack routines is linked, not the essl version. However
> the fft and blas from essl are linked (unless there is a
> copy of blas into lapack, which shouldn't be the case).
> The resulting loss of performances should be minor.
> If fft and blas from essl are not linked, the loss of
> performances is much larger.
>
> Final clarification:
>
> -D__ESSL means that the fft routines of essl are used, and
> that the calls of some lapack routines follow the essl syntax,
> not the lapack syntax;
>
> -D__LINUX_ESSL means that the fft routines of essl are used,
> and that the calls of lapack routines follow the lapack syntax.
>
> In all cases, it is convenient to link essl before lapack (essl does
> not contain all lapack routines, just a subset, so not linking lapack
> may result in missing symbols). If the lapack replacements in essl
> do not follow the lapack syntax (IBM SP machines, typically),
> -D__ESSL should be used. If they follow the lapack syntax, or if
> they do not contain lapack replacements (IBM BlueGene and other
> strange IBM machines), -D__LINUX_ESSL should be used.
>
> Complicated? blame the geniuses who wrote lapack replacements
> with the same names but called in a different way
>
> P.
> ---
> Paolo Giannozzi, Dept of Chemistry&Physics&Environment,
> Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
> Phone +39-0432-558216, fax +39-0432-558222
>
>
>
>
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