I checked that two gpu were installed.
case 1 :
device-id = 0
device-id = 1
Through the above command, it was confirmed that the two gpu were calculated respectively.
However, parallel calculations are not performed through the local-rank command. What is this error message associated with, and how can it be resolved?
The error message is very clear; you are only running with a single MPI rank whereas you need to be running with two.
While you may think you are running with two ranks due to mpiexec -n 2 pyfr ... this is likely because mpiexec belongs to a different MPI library to that which mpi4py was compiled against. For example, if mpiexec comes from MPICH but mpi4py was compiled against OpenMPI. You can not mix and match MPI runtimes: pick one and stick with it. Before running PyFR it is also suggested to try some of the mpi4py example programs.