METIS - Serial Graph Partitioning and Fill-reducing Matrix Ordering, is a set of serial programs and libraries for partitioning graphs.
For our unstructured ocean mesh we utilize METIS to distribute the computation of the whole ocean to any number of processes, i.e. 3600 processes would require a mesh partitioned to 3600 pieces. In our case, the METIS-graph is the surface of the unstructured FESOM ocean mesh, i.e. a list of connected mesh points. METIS is now fed with this mesh information and the desired number of parts.
METIS is able to take in to account different “costs” for mesh points and for cutting edges. This way one can give it a hint to be able to regard higher computational costs for i.e. deep ocean. The edges cut by METIS represent our network communication that is taking place during the distributed computation, which is desired to be as low as possible.