Re: Reported any bugs in C-LAPACK routine DSPEVX?

From: Andreas Krebs (krebs.andreas_at_gmx.de)
Date: 10/29/04 

Date: Fri, 29 Oct 2004 12:42:33 +0200

Javier Almeida wrote:
> Thank you Andreas for your great explanation.
> It really surprised me that the steps you explain in your post are
> exactly the same I have to do to link against CLAPACK, the only
> difference being the libraries you tell the compiler to link against.
> Even the underscore you add to de name of the routine is also the same
> in CLAPACK, and of course the way you pass by reference the arguments
> is also the way to proceed in CLAPACK. I also like to embed the
> CLAPACK routines declarations in my programs instead of using the
> given .h headers (and you're right:in C++ you should embrace this
> declarations within an extern "C" {} directive)...Now it's not clear
> to me which is then the difference between linking agaisnt CLAPACK or
> using directly LAPACK, as both ways differs only in the final
> libraries you link against (¿?).

I think this is the difference. When linking to CLAPACK
you link to a library which was C-compiled
after transforming the original fortran code into C by using f2c.
Look http://www.netlib.org/clapack/faq.html ...
" 1.1) What is CLAPACK?
The CLAPACK library was built using a Fortran to C conversion utility
called f2c. The entire Fortran 77 LAPACK library is run through f2c to
obtain C code, and then modified to improve readability. CLAPACK's goal
is to provide LAPACK for someone who does not have access to a Fortran
compiler."

When linking to LAPACK you link to a library which was build by
compiling the fortran code directly. So, CLAPACK is quite useful if you
do (not have a fortran compiler or only a bad fortran compiler) and you
are eager to use only self compiled libraries.

Programming C++,
http://math.nist.gov/lapack++/
is maybe interesting when using several lapack routines. Using only a
few installation of the package seems more complicated to me than the
direct approach. I tried TNT also a few years ago, but it did not
convince me.

Regards, Andreas

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