Mpiexec is a replacement program for the script mpirun, which is
part of the MPICH package. It is used to initialize a parallel job
from within a PBS batch or interactive environment. Mpiexec uses
the task manager library of PBS to spawn copies of the executable
on the nodes in a PBS allocation.

WWW:	http://www.osc.edu/~djohnson/mpiexec/index.php