/usr/local/opt/llvm/bin/clang -fopenmp -L/usr/local/opt/llvm/lib main.c -o a
./a
The best performance is achieved when the number of nodes is equal to number of cores. E.g.:
$HOME/opt/usr/local/bin/mpicc -o pi ./mpi_pi.c
$HOME/opt/usr/local/bin/mpirun -np 4 ./pi
MPI
MPI Reduction
MPI Send & Receive