[mod4 (modulepath)]$ module purge
[mod4 (modulepath)]$ module load pgi/19.4
[mod4 (modulepath)]$ module load openmpi
[mod4 (modulepath)]$ module list
Currently Loaded Modulefiles:
 1) pgi/19.4   2) openmpi/4.0
[mod4 (modulepath)]$ mpirun
mpirun (openmpi/4.0, pgi/19.4)
[mod4 (modulepath)]$ module switch --auto pgi intel/2019
Switching from pgi/19.4 to intel/2019
  Unloading dependent: openmpi/4.0
  Reloading dependent: openmpi/4.0
[mod4 (modulepath)]$ module list
Currently Loaded Modulefiles:
 1) intel/2019   2) openmpi/4.0
[mod4 (modulepath)]$ mpirun
mpirun (openmpi/4.0, intel/2019)
[mod4 (modulepath)]$ module switch --auto intel intel/2018
Switching from intel/2019 to intel/2018
  ERROR: Unable to locate a modulefile for 'openmpi/4.0'
  WARNING: Reload of dependent openmpi/4.0 failed
  Unloading dependent: openmpi/4.0
[mod4 (modulepath)]$ module list
Currently Loaded Modulefiles:
 1) intel/2018
[mod4 (modulepath)]$ mpirun
mpirun: command not found
