Set (DAMASK) environment to use fewer ranks than cores

[gcapes]

As a user, I would like to be able to set the number of mpi ranks independently from the number of cores requested for a workflow task, so that I can have more memory for the task.

On CSF3, one approach to requesting (a bit) more memory for your batch job is to request more cores. https://ri.itservices.manchester.ac.uk/csf3/batch-slurm/high-memory-jobs-slurm/

mpirun can detect how many cores have been allocated by SLURM and use that for the number of ranks without explicitly using mpirun -n $SLURM_NTASKS. This may lead to errors if you want to use e.g. 10 cores/ranks with more memory than default, but have requested e.g. 20 cores in order to get more memory.

A hacky workaround would be to set mpirun -n XX in the MatFlow environments file but this would need to be changed per workflow.