[Developers] reduction integration operator....

Erik Schnetter schnetter at cct.lsu.edu
Wed Oct 5 11:03:56 CDT 2005

On Oct 5, 2005, at 10:54:24, Francisco S. Guzman wrote:

> Hi all,
> I was wondering whether there is an integration reduction operator in
> PUGH.... if not: I wonder whether it would be worth implementing one
> (any similar suggestions from someone else about this?)....

The "sum" operator is the integration operation.  With PUGH, you have  
to pay attention to boundary effects, especially with symmetry  
boundaries.  Carpet handles boundaries (outer, symmetry, refinement)  
correctly, so that the result of the "sum" operation is (almost) what  
you expect:

     M = sum [rho] dx^3

That is, the total mass is the sum over the density times the  
(coarse) grid volume.

> Suggestion: an example on how to use the reduction operator in  
> fortran is
> missing, and actally among many thorns it is really a pain to find one
> example where 'sum" (for instance) is used, EHFinder is the only one I
> could find.....

Whisky should be another good place to look.

The reduction operators are just about being changed, so that they  
are more consistent to call.  This should be finished in a few weeks.

The thorn CactusTest/TestGlobalReduce shows how to call reduction  
operators from C.  Calling them from Fortran is very similar, but I  
guess we could translate the file ourselves -- that would also be a  
good test of the Fortran interface.

Thanks for your suggestion,
is there any code in particular that we can help you with?

Erik Schnetter <schnetter at cct.lsu.edu>

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