Developping and building MPI programs

An excellent tutorial and resources can be found here (look for English version) : http://www.idris.fr/formations/mpi/
Only few tips and examples are provided here because the IDRIS tutorial is more than enough to learn MPI.

(Many thanks to Adrien Cassagne who translated to C the Heat equation and the Conjugate gradient)

• Fortran and C : Hello World !
• Fortran : Bruteforce
• Fortran and C : Ping Pong (Send/Recv)
• Fortran and C : Switch (SendRecv)
• Fortran and C : Grouped Calculations (All*)
• Fortran and C : Blur 1D
• Fortran and C : Cartesian Communicator
• Fortran and C : Heat Equation 2D
• Fortran and C : Conjugate Gradient

First, you need to install a working mpi tool chain. If you are on a workstation, you may need to build it yourself. Copy/past the following lines into your shell, it will build a ready to use mpi environment (note that you can change the 1.6.4 (and v1.6 for download URL) number by the last version, check on openmpi web site, http://www.open-mpi.org/ , top right, stable release) :

wget http://www.open-mpi.org/software/ompi/v1.6/downloads/openmpi-1.6.4.tar.gz
tar xvzf openmpi-1.6.4.tar.gz
cd openmpi-1.6.4
./configure --prefix=$HOME/openmpi/1.6.4 CC=gcc CXX=g++ F77=gfortran FC=gfortran
make
make check
make install
export PATH=$HOME/openmpi/1.6.4/bin:$PATH
export LD_LIBRARY_PATH=$HOME/openmpi/1.6.4/lib:$LD_LIBRARY_PATH

Now, you should have a working mpi system. Try it using :

mpirun --version

And you should get :

mpirun (Open MPI) 1.6.4
Report bugs to http://www.open-mpi.org/community/help/

Do not forget that if you want to make it persistent, you have to add :

export PATH=$HOME/openmpi/1.6.4/bin:$PATH
export LD_LIBRARY_PATH=$HOME/openmpi/1.6.4/lib:$LD_LIBRARY_PATH

In your .bashrc.

The example here is the hello world seen before.

Compile it using the mpif90 wraper (if you type mpif90 –version, you will see it's just a wraper of gfortran) :

mpif90 hello-mpi.f90 -o hello-mpi

Then execute it, using 4 processes (you can load as many processes you want on a single computer. You will get max performances if you have one process per core. DO NOT use more than 64 processes on a single machine, it may freeze and you may be force to reboot the OS manually).

mpirun -np 4 ./hello-mpi
 
Hello world ! I am process 0 on 4 processes.I am running on tallgeese
Hello world ! I am process 3 on 4 processes.I am running on tallgeese
Hello world ! I am process 1 on 4 processes.I am running on tallgeese
Hello world ! I am process 2 on 4 processes.I am running on tallgeese

For C code, use mpicc (or mpic++ for C++) instead of mpif90.