Fix slow performance with multiple sims

[tahorst]

I've noticed extremely slow simulation times when running multiple sims at the same time on my local machine. In case anyone else has been running into this issue, it can be fixed by setting the number of threads for OpenBLAS: export OPENBLAS_NUM_THREADS=1 before running. This will likely be machine dependent and might not affect everyone but we might want to consider setting up the environment to set this by default. Restricting OpenBLAS to one thread didn't seem to affect performance.