[Users] GF information question

[Erik Schnetter]

On Thu, Nov 19, 2015 at 11:05 PM, Frank Loeffler <knarf at cct.lsu.edu> wrote:

> 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).
>

There is no need for a distributed grid array. After counting locally, a
"local reduction" (i.e. reduction of a local variable) gives you the
overall result.

-erik

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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-- 
Erik Schnetter <schnetter at cct.lsu.edu>
http://www.perimeterinstitute.ca/personal/eschnetter/
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