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Zero is a cluster system and so message passing libraries are used to make code run in parallel. There are several different libraries installed. Shared memory parallelization (OpenMP, provided by the autoparallelizing options on some of the compilers) can also be used for up to eight cores but not further.

The available message passing libraries are MPI implementations: currently we have OpenMPI built for Intel and GNU compilers.

To change your parallel environment you need to load the appropriate module. By default OpenMPI with Intel compilers is loaded. To switch you'd edit your .bash_profile file and change the module add line.

Compile your code with the MPI compilers. These are usually called mpicc, mpicxx, mpif77 and mpif90.

To run MPI code you normally use a command such as mpirun to launch your program. The version of mpirun on zero will talk to the queueing system and automatically work out the number of cpus assigned to the job and which nodes to use which makes it very simple to use. There are some examples of use in /info/slurm.

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