###### tags: `Classical Computing` # MPI (select,ncpus,-np) MPI is a module for parallel calculations. The following is shell script used when MPI calculations. ```shell= #PBS -l select=2:ncpus=96 mpiexec -np 128 python $INPUT ``` This page is aimed at understanding numbers appear (select,ncpus,-np) in the script. ## select "select" is number of nodes selected. ## ncpus `ncpus` stands for number of CPUs per node, which effects the memory that can be used. > CPU (Central Processing Unit). > How can we look up the maximum `ncpus`? ## -np "mpiexec -np" stands for number of jobs that are parallelized during the calculations. > Large number of `-np` takes much time since many jobs needed to be parallelized with same number of CPUs. Thus `-np` is recomended to be small as possible. ## References https://blog.codecamp.jp/visual-studio-ocde