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A general rule of thumb is that the number of cells assigned to a given core should be in the order of some thousands. A minimum of approximately 1,000 cells is needed to make an MPI computation worthwhile. An individual core would be expected to be assigned from 500 to 10,000 cells. 20,000 cells should be the maximum number of cells on any one core. For example, if we have a hydrodynamic model with 60,000 cells and 6 cores, then the model could initially be divided into six subdomains, each with 10,000 cells. The user should then adjust the run configuration by increasing or decreasing subdomains.
2. Number of constituents
Beside Besides hydrodynamics, each transport process added to the simulation such as salinity, temperature, dye, sediment, toxic, or water quality parameters, requires more equations to be solved. Although the processing of the constituents in each sub-domain can be parallelized using OMP, if more constituents need to be considered, then it is recommended that more domains be used.
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The goal of the modeler should be to ensure that an equal computational load is place placed on each processor. This means that if some models have different numbers of layers in different parts of the grid, thought should be given to how to divide the domain. For example, a Sigma-Zed model could fewer layers in some parts of the domain. The domain should then be divided in such a way that more horizontal cells are in that one sub-domain so that the total number of vertical and horizontal cells are roughly equal for each sub-domain.
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