## 2.1. Parallelization of Structured Part Calculations

Domain Decomposition is used to parallelize the structured Part computations performed by all solvers which utilize an IJK mesh. Using this method, each part is divided along index planes in the I, J and K directions (J and K directions for Shell parts) to form smaller parts called sub-domains. At the present time, users must define the domain decomposition manually to be used for each problem they wish to run in parallel.

These sub-domains are distributed among the CPUs of the parallel machine using an algorithm that attempts to minimize inter-CPU communications and balance the computational load on each machine. Each sub-domain is processed in parallel as if it were a standard part in serial processing. This importantly allows most of the source code for serial processing to be used without modification.

Because the part structure does not normally change during simulations, a static decomposition of the entire index space is usually sufficient to achieve good parallel performance.

Efficient parallel processing of the Part calculations requires not only good load-balancing of the computation, but also the efficient exchange of data at sub-domain boundaries. This is best achieved by users clearly understanding the process involved and choosing their domain decompositions to suit the specific host configuration they intend to use.

Automatic decomposition can be used to decompose Euler-FCT Parts using the recursive bi-section method described below.

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