Using GotoBLAS2 in a MATLAB MEX file (shared library help?)

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Thomas McLaughlin
Thomas McLaughlin on 15 Jul 2011
Hi,
I have been having a lot of trouble using the GotoBLAS2 library with a C program, which I want to call via the MEX interface.
Basically, I have some numerical optimization code in C that I want to use in a MATLAB script. I am trying to link the code to GotoBLAS2 for a fast BLAS library. Based on an example I saw of the use of this code, I am compiling it with the linker options
-llapack -lgoto2
to link it with GotoBLAS2.
I have a separate stand-alone program (non-MEX) which compiles this way and works fine. However, when I compile the MEX version and then run it, the LAPACK functions I call end up going to the MATLAB LAPACK libraries, which do not seem to be compatible. For example, my code contains a LAPACK call such as
int work_sz = -1; dsytrf("U", (int *)&m, NULL, (int *)&m, NULL, (LM_REAL *)&tmp, (int *)&work_sz, (int *)&info);
I understand this code is supposed to make a direct call to a FORTRAN library, since C and FORTRAN have the same calling conventions (?), and in my stand-alone program it works. However, if I execute the same call using MATLAB's gdb debugging, I see the error
MKL ERROR: Parameter 7 was incorrect on entry to DSYTRF.
This tells me that the "dsytrf_" symbol is actually being loaded from the Intel Math Kernel Library (which comes with MATLAB) instead of the LAPACK my stand-alone program uses (which is in /usr/lib/liblapack.so). So my question is this: how can I choose which LAPACK library my MEX-ified program uses?
Note: to make things more complicated, when I compiled GotoBLAS2, I set it to statically link a version of LAPACK it came with. When I execute "nm libgotoblas2.so", I see that it actually contains a symbol called "dsytrf_" as well. So I guess I would be happy if my MEX program used either the function in some separate LAPACK, or this one in libgotoblas2.so.
Many thanks for any help!

Answers (1)

Stephen Becker
Stephen Becker on 22 Feb 2012
Matlab is probably adding a -lmwblas flag somewhere, so their version of blas is overriding yours. You can probably edit mexopts.sh and change this.
Also, try http://www.stanford.edu/~echu508/matlab.html. He has an interesting method to change the version of BLAS that Matlab uses. Basically, for him (he was on a Mac), he edited this file: /Applications/MATLAB_R2008b.app/bin/maci/blas.spec
Best of luck!

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