I want to use openblas as backend of blas in Eigen. Is it possible? Thank you!

Yes, this should be possible: just compile with -DEIGEN_USE_BLAS and link to openblas.

See http://eigen.tuxfamily.org/dox-devel/To ... elMKL.html for the details.

Well, this does not seem to work with Eigen 3.2.2. First of all, the CMakeFiles.txt file would have to be changed to add the -DEIGEN_USE_BLAS definition:

Code: Select all

add_definitions(-DEIGEN_USE_BLAS -DEIGEN_USE_LAPACKE)

Anyway, when I define EIGEN_USE_BLAS before the Eigen headers are included:

Code: Select all

#define EIGEN_USE_BLAS
#include <Eigen/Dense>


I get a fatal error during compilation because the header file mkl.h could not be found. But I don't want to use Intel MKL's library, but OpenBLAS.

Can Eigen really link to OpenBLAS (or any other BLAS library)?

It's not possible yet in Eigen (version 3.2..
You can refer to this post: viewtopic.php?f=74&t=123117

indeed, you really need to grab the devel branch, not even 3.3-beta1 !

Does OpenBlas makes things faster when in used?

Which functions of Eigen will use OpenBlas instead of the built in functions?

Thank You.

All "large enough" matrix-matrix and matrix-vector products (including triangular and symmetric matrices) will call the underlying BLAS implementation, that might be faster than Eigen's built-in ones with multi-threading. For sequential uses, speed should be in par.