Steps in Choosing Problem Sizes
1. Appeal to higher powers
May know that users care only about a few problem sizes
But not generally applicable
2. Determine range of useful sizes
Below which bad perf. or unrealistic time distribution in phases
Above which execution time or memory usage too large
3. Use understanding of inherent characteristics
Communication-to-computation ratio, load balance...
For grid solver, perhaps at least 32-by-32 points per processor
40MB/s c-to-c ratio with 200MHz processor
No need to go below 5MB/s (larger than 256-by-256 subgrid per processor) from this perspective, or 2K-by-2K grid overall