Graph partitioning

The mpas_tools.seaice.partition module contains a function for creating graph partition files for MPAS-Seaice that are better balanced than those created from Metis tools directly.

Graph partition tools

The tools prepare_seaice_partitions and create_seaice_partitions are used to create MPAS-Seaice graph partitions that are better balanced so that each processor “owns” cells from both polar and equatorial regions.

$ prepare_seaice_partitions --help
usage: prepare_seaice_partitions [-h] -i MESHFILENAMESRC -p FILENAMEDATA -m
                                 MESHFILENAMEDST -o OUTPUTDIR

Perform preparatory work for making seaice partitions.

  -h, --help            show this help message and exit
                        MPAS mesh file for source regridding mesh.
                        Input ice presence file for source mesh.
                        MPAS mesh file for destination regridding mesh.
                        Output direct

The input mesh file contains the MPAS-Seaice mesh fields for the mesh used to create the “presence” file. The “presence” file itself contains an icePresence field that indicates where sea ice might be present. We typically use a 60-km mesh file and the corresponding presence file. The presence file will be regridded to the given output MPAS-Seaice mesh. Here the ice presence was determined as any cell in the mesh to have had ice present at any time during a 50 year MPAS-Seaice standalone simulation with the above 60-km mesh file. The output directory is often the current directory.

After this preprocessing has finished, the create_seaice_partitions tool can be run one or more times. It is significantly more efficient to provide a list of processor numbers than to call the tool for each processor number separately.

$ create_seaice_partitions --help
usage: create_seaice_partitions [-h] -m MESHFILENAME -o OUTPUTDIR
                                [-c MPASCULLERLOCATION] [-p OUTPUTPREFIX] [-x]
                                [-g METIS] [-n NPROCS] [-f NPROCSFILE]

Create sea-ice partitions.

  -h, --help            show this help message and exit
                        MPAS mesh file for destination regridding mesh.
                        Output directory for temporary files and partition
                        Location of MPAS MpasCellCuller.x executable.
                        prefix for output partition filenames.
  -x, --plotting        create diagnostic plotting file of partitions
  -g METIS, --metis METIS
                        name of metis utility
  -n NPROCS, --nProcs NPROCS
                        number of processors to create partition for.
                        number of processors to create partition for.

The mesh filename provides the desired MPAS-Seaice mesh, the same as the destination mesh for prepare_seaice_partitions. The output directory is often the current directory. A directory containing the MpasCellCuller.x tool can be provided but by default it will be found in your path as part of the mpas_tools conda package. The output prefix will be prepended onto each graph partition file, and defaults to The Metis tool is nearly always gpmetis, the default, and must be available in your path (which is the case if you use mpas_tools conda package). One graph partition file is created for each number of processors (one or more integers) provided. Alternatively, these can be listed, one value on each line, in a file. You can optionally save a NetCDF file with partition information, which will contain a partition_{nProcs} field for each number of processors requested.

Graph partition function

A helper function mpas_tools.seaice.partition.gen_seaice_mesh_partition() is used within create_seaice_partitions. It can also be called directly but must already have the files resulting from prepare_seaice_partitions available in the output directory.