Hi Jerry,
Your guess about magic numbers is correct.
If you want to do your own preconditioning, I think the simplest way is
to run GRIDXPND (select "Grid | X-Utilities | Expand Grid"). Enter
"0.01" for Minimum % to Expand Grid and "RECTANGLE" for shape of output
grid. This will expand your grid the minimum amount to reach the
"magic" dimensions.
You then need to run GRIDFILL (select "Grid | X-Utilities | Fill Grid
dummies") to fill the dummy values in the cells added to the grid. Note
that FFT2IN will NOT complain if you have dummy cells. However, the
results will NOT be correct.
If you want to force all the new cells in the expanded grid to exactly
zero, enter a distance smaller than the cell spacing for "Distance at
Which to Roll to 0", 0 for "Roll Off Base", and 0 for "Number of
Convolution passes".
Cheers,
Gerry Connard
--
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