Problem with MPI process

[Former user]

I encountered the same problem as Issue #1857. However, since I am new to the Einstein Toolkit, I don't quite understand the solution there. How do I change the MPI process to be 2? Do I just use '--procs=4 --num-threads=2' in the command? PS: I am trying the command of "!./simfactory/bin/sim create-run inspiral_d06_lres --parfile=par/inspiral_d06_lres.par --procs=4". This doesn't work and give the same error message as Issue #1857.

[Roland Haas]

Yes, using --procs=4 --num-threads=2 will work for you. For historial reasons --procs really means "number of cores to use". Simfactory has some idea of how many threads per MPI rank one is to use by default and currently, on a laptop that numbers "as many threads as the laptop has cores". simfactory will only create more than 1 MPI rank of more cores ("procs") than threads are requested. Using --num-threads explicitly tells simfactory how many threads to use per MPI rank. The number of MPI ranks used is then procs / num-threads ie 2 in your example with both --procs and --num-threads and likely 1 without --num-threads if you workstation has more than 4 cores.

To know for sure you would have to inspect your laptop's machine.ini file in simfactory/mdb/machines/ (it will be named after the hostname of your laptop ie the name that simfactory/bin/sim whoami outputs).