[Users] GF information question

[Frank Loeffler]

On Fri, Nov 20, 2015 at 04:41:48AM +0000, Garrison, David wrote:
> How do you find the number of non-zero elements in a Grid Function in Cactus?

The best way would probably be to count them locally on each process,
write the result in a distributed grid array, and do the sum there by
syncing the array and counting locally (not sure if a reduction on such
an array would work, it might).

Another, but more expensive way (in terms of memory size and memory
accesses) would be to create another grid function, populate it with
either 1 or 0 depending on the non-zero-property of the GF you are
interested in, and calling the existing sum-reduction on it.

Frank

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