For more information, please consult the official documentation OpenMPI
# Install OpenMPI in operating systems based on ArchLinux
$ sudo pacman -S openmpi
# compile
$ mpicc -lm yourfile.c -o yourapp
# running
$ mpirun -np <numberproccess> yourapp
You can read more in CUDA, Installation guide
# Install CUDA in operating systems based on ArchLinux
$ sudo pacman -S cuda
# compile
$ nvcc yourfile.c -o yourapp
# running
$ ./yourapp