anchor.diff:    doCheck = true;
     checkPhase = ''
       export PYTHONPATH="$out/lib/${python.libPrefix}/site-packages:$PYTHONPATH"
  -    python3 << EOF
  +
  +    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),
  
positive.code:     numpy
      scipy
      matplotlib
      h5py
      cython
      autograd
      mpi4py
  
negative.code:                     resolution=resolution)
      sim.run(until=200)
      EOF
  
      ${mpi}/bin/mpiexec -np 2 python3 test.py
    '';
  
    meta = with lib; {
  