Dear Debian Science Team,

when trying to exchange libblis2-pthread for libopenblas0-pthread,
I get the following error from a self compiled program (using libopenblas-dev):

  /usr/lib/x86_64-linux-gnu/libblas.so.3: undefined symbol: openblas_set_num_threads

The library is actually /usr/lib/x86_64-linux-gnu/blis-pthread/libblas.so.3.

I'm not quite sure which package is to blame for this and if the
libraries are intended to be interchangeable at all.
Can you help me?

Regards,
Jörg.

Hi Jörg, your error refers to openblas, which is a separate BLAS
implementation from blis.  The implementations are compatible, but
only when built against libblas.so using -lblas, i.e. when using the
common BLAS ABI.

The appearance of the openblas symbol suggests that your applications
were built using -lopenblas instead of -lblas, enabling some
openblas-specific symbols to be called in.

You've got two options,

1) rebuild your binaries (and to protect from the same problem in the
   future, ensure they link strictly against -lblas)

2) install OpenBLAS instead of BLIS (e.g. install libopenblas-pthread-dev)
   Together with that you'd probably want to check that the blas
   alternatives match, running both
     sudo update-alternatives --config libblas.so-x86_64-linux-gnu`
   *and*
     sudo update-alternatives --config libblas.so.3-x86_64-linux-gnu