anchor.diff:  { stdenv, lib, buildPythonPackage, fetchFromGitHub, autoreconfHook, pkg-config
  -, gfortran, mpi, blas, lapack, fftw, hdf5-full, swig, gsl, harminv, libctl
  +, gfortran, mpi, blas, lapack, fftw, hdf5-mpi, swig, gsl, harminv, libctl
   , libGDSII, openssh, guile
   # Python
  -, python, numpy, scipy, matplotlib, h5py, cython, autograd, mpi4py
  +, python, numpy, scipy, matplotlib, h5py-mpi, cython, autograd, mpi4py
   } :
   
   buildPythonPackage rec {
  
positive.code:     numpy
      scipy
      matplotlib
      h5py
      cython
      autograd
      mpi4py
  
negative.code:   doCheck = true;
    checkPhase = ''
      export PYTHONPATH="$out/lib/${python.libPrefix}/site-packages:$PYTHONPATH"
  
      export OMP_NUM_THREADS=1
  
      # Fix to make mpich run in a sandbox
      export HYDRA_IFACE=lo
      export OMPI_MCA_rmaps_base_oversubscribe=1
  
      # Generate a python test script
      cat > test.py << EOF
      import meep as mp
      cell = mp.Vector3(16,8,0)
      geometry = [mp.Block(mp.Vector3(mp.inf,1,mp.inf),
  