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Run the script as a single slot job on a specific idle host, for example: "bsub -q mpitest -m bullet0019 ./mploadtest.csh" . Open up a terminal session on the chosen host and observe the load across the CPU cores. You can do this running "top" in interactive mode and pressing "1" for the per-core load view. You'll notice the child processes associated with your running job are distributed across several cores, even though the job is "single-slot".
Wait for the job to finish then resubmit to the same host but this time request CPU affinity: "bsub -q mpitest -m bullet0019 -R 'affinity[core:membind=localprefer]' ./mploadtest.csh". Observe this job again using the per-core load view with top. This time you should see all of the load is associated with a single core. The number of assigned cores will match the number of job slots so submitting the job with "-n 3" will result in the job using 3 CPU cores.