Running MPI Programs
LAM MPI version, Fall 2003

1. Create a "host file":
   • name this file "lamhosts", for instance:
     yourcomputer.tjhsst.edu
   • Normally you would list other computers to connect with,
     because of security issues, we are currently limited to only one workstation

2. Enable the LAM Mpi system:
   • lamboot -v lamhosts
     ("lamhosts" is the name of your hostfile from #1 above)

3. Compiling your MPI program:
   • C version: mpicc.lam -o filename filename.c
     (the executable file will be "filename")
   • C++ version: mpiCC.lam -o filename filename.cpp
     (the executable file will be "filename")
   • NOTE: cin DOES NOT WORK, use scanf
   • For MATH FUNCTIONS - use "-lm" on the command line
     (this loads the math library)

4. Run the executable file:
   • mpirun.lam -np 5 filename
     This runs your program on 5 processes, "-np" specifies "number of processes"
   • more information at Running LAM/MPI
     Also see "mpirun -c and mpirun -np -- what's the difference?"

5. IMPORTANT - when you're done, MAKE SURE TO HALT MPI:
   • lamhalt
   • otherwise you leave extra processes running on your workstation!