Re: mex file linking

[Matyas Sustik]

I think I need to clarify my questions; I am admittedly a bit confused
about the use of libraries in octave.  Comments would be appreciated.

The way I understand this now is that octave has lapackgf-3 compiled
into it (this is a university CS machine and I do not know the install
details yet).  I suspect that when my C++/MEX code calls an LAPACK
function it will use a version available from this LAPACK that was
specified by the admins at install time.

It is confusing that mkoctfile -v indicates that linking is explicitly
done with -llapackgf-3, however if I just use the link command
directly and remove that library, I still get working code; so the
LAPACK functions come from a library from within octave or such.  Say,
if LAPACK is upgraded on that machine I am not sure what version of
LAPACK will be used.

Furthermore, it seems that I am not able to specify an *alternate*
library to be used for the LAPACK functions.  I tried to specify
-lmwlapack (before -loctave) hoping that I could get the same version
as Matlab uses (used -L... etc.) but that does not appear to work.

I do not know whether and/or why the LAPACK would be different for
Matlab and Octave on this machine.  (Would not make much sense I
think.)  I need to release the code for Matlab, because that is still
somewhat expected, however I would prefer to use Octave and it would
be nice if I could exactly reproduce a Matlab run on Octave.

I also plan to make a new version of some LAPACK functions.  I do not
intend though to recompile the whole LAPACK library.  Can I just
replace some selected functions?

Thanks in advance.
-Matyas

On Tue, Dec 13, 2011 at 10:36 PM, Matyas Sustik <address@hidden> wrote:
> Hi All,
>
> I am linking a mex file (for octave) with:
>
> g++ $^ -o $@ -shared -Wl,-Bsymbolic $(OCTAVE_LIBS) -loctave -lcruft
> -llapackgf-3 -lblas-3gf -lfftw3 -lfftw3f -lreadline -lncurses -ldl
> -lhdf5 -lz -lm -lgfortranbegin -lgfortran -lasm -L.
> (OCTAVE_LIBS = $(shell mkoctfile -p LFLAGS)
>
> (I am not sure whether all the libraries are needed, but mkoctfile -v had 
> them.)
>
> I definitely need blas and lapack in my code.  However, if I link
> without them I still get working code!!  How is that possible??  Does
> octave provide the blas and lapack functions by default?
>
> Thanks!
> -Matyas