[IPOL discuss] Clapack and cblas libraries interfacing

[Pierre Moulon]

Thanks for sharing your experiments

at the risk of repeating myself:

I do not understand why Eigen could not be considered as a good math
library for Ipol.

http://eigen.tuxfamily.org/index.php?title=Main_Page
With such a library : High Level matrix or some Blas function could be used.
Using High Level code made the code easier to read, to review and so better
for a Research code.

And unfortunately GSL is not officially supported by windows.

-- 
Regards/Cordialement,
Pierre M

2012/3/29 Tristan Dagobert <tristan.dagobert at cmla.ens-cachan.fr>

> Hello,
>
> I would like to share my recent experience
> about linking cblas and clapack librairies (two of the authorized libraries
> in the guidelines 1.00) with a IPOL program, because this leads some
> remarks and
> questions.
>
> There are currently at least 3 versions of C prototypes for CBLAS and
> CLAPACK,
> linking the C functions with the Fortran binaries :
>
> (1) the version installed by default, with the ATLAS packages, upon the
> differents Linux systems
>   (like the FUCHSIA server) containing :
>  - clapack.h (a file of 149 lines) with only few prototypes to Lapack
> Fortran binaries;
>  - cblas.h containing all prototypes to Fortran routines.
>
> (2) the version from sources lapack 3.2.1 compatible with Windows :
>  - clapack.h (a file of more than 7200 lines) with all the prototypes to
> Fortran binaries;
>  but this does not come with the cblas.h file, which must downloaded too
> in CBLAS.tgz.
>
> (3) the version from sources lapack 3.4.0 compatible with Windows :
>  - lapacke.h with all the prototypes to Fortran binaries;
>  but this does not come with the cblas.h file, which must downloaded too
> in CBLAS.tgz;
>
> The problem is these versions do not share the same C prototypes. For
> example, to use the Fortran routine of SVD named dsyevd() :
>
> - (1) --> the prototype simply does not exist in clapack.h
>         but binary code is present in libclapack.a (!!);
> - (2) --> clapack_dsyevd() is C-prototyped in clapack.h;
> - (3) --> LAPACKE_dsyevd() is C-prototyped in lapacke.h;
>
> According to differents lapack forums, the C prototypes of 3.4.0 version
> are intented to replace at mean term, the actual format (1).
>
> Consequently, stability of C APIs of clapack seems not to be safe.
> Building a IPOL program with the current default prototypes (1) will lead
> to restrict
> its portability et its simplicity of installation even upon Linux systems,
> from 5 to 10 years.
> In addition, the installation from sources, of the (2) and (3) librairies
> is quiet subtile and tricky (gfortran compilers, f2c ...) and needs
> certainly more time than a final user of an IPOL program should expect.
>
> So my questions are :
> - Is there a reference version of Clapack, Cblas defined in the IPOL
> guidelines ?
> - What about the GSL library, which owns more stable prototypes (it is
> natively
> written in standard C and does not need Fortran conversion)s. Is its
> integration
> planned for the next guidelines as a possible alternative as external
> library ?
>
> Regards.
> Tristan
>
>
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