12.5.3 The barotropic solution

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12.5.3 The barotropic solution

The 2-D barotropic equation is divided into tasks in the same way as was done for the prognostic equation. Since the processor boundaries are the same, communication involves the same rows. Each processor dimensions arrays for only that part of the domain being worked on by the specific processor and the actual memory requirement is small. Therefore, within each processor's task no memory window is needed. All indexing into 2-D arrays is in terms of the absolute global index ``jrow''.

figure=decomp.ps,height=8.0in

**Figure 12.1:** a) A 2d domain decomposition using 9 processors. b) Rearranging the 9 processors for a 1d domain decomposition in latitude. c) Comparison of 1d and 2d domain decomposition giving number of communication calls and words transferred for 9, 100, and 900 processors.
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**Figure 12.2:** a) Integrating prognostic equations using 3 processors and 2nd order numerics. b) Task limits ``jstask'' and ``jetask'' as well as row limits ``jscomp'' and ``jecomp'' for each processor.
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**Figure 12.3:** a) Integrating prognostic equations using 3 processors and 4th order numerics. b) Task limits ``jstask'' and ``jetask'' as well as row limits ``jscomp'' and ``jecomp'' for each processor.
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Next: 13. Database Up: 12.5 Domain Decomposition Previous: 12.5.2 Communications

RC Pacanowski and SM Griffies, GFDL, Jan 2000