[Users] global reductions in specified domains

[Vassilios Mewes]

Hello Roland,

another question on this topic i am trying to wrap my head around:

actually, i am not performing those processor local "integrals" on grid
variables, but the result is a new variable (i just chose rho in the
example pseudocode i wrote on friday)

now my problem is the scheduling...

i have different radial shells, and a function that computes the
"processor-local" value of the quantity i want to sum (which is defined as
a type=scalar in my interface.ccl...

in order to be able to do that, i need to schedule my thorn as global
loop-local, otherwise i get failed assertions in the loop macros..

now my question is the following:

how can i now perform the reduction on this "processor-local" quantity?

if i write a new function, will it have access to all the instances every
processor creates?

if i calculate the reduction inside the "processor-local" function, will it
work? because the function is global loop-local and i will need a loop to
perform the integration on every shell i specify..

i tried to manually change modes using the carpet c++ macros, but that has
led to segmentation faults only so far...

any idea how i could do that?

best wishes,

Vassili


On Fri, Nov 15, 2013 at 7:45 PM, Vassilios Mewes <vassilios.mewes at uv.es>wrote:

> Thanks a lot, I will try this!
>
> best wishes,
>
> Vassili
>
>
> On Fri, Nov 15, 2013 at 5:39 PM, Roland Haas <rhaas at tapir.caltech.edu>wrote:
>
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>> Hello Vassilios,
>>
>> > and then reduce over all radial shells
>> >
>> > for(int iradii=0; iradii < nradii; iradii ++) {
>> > CCTK_Reduce(cctkGH,-1, &rho_total_shell[iradii], CCTK_VAR =
>> > rho_in_shell[iradii]) }
>> >
>> > would that be an option? or even work?
>> Yes, that is essentially option 2 that I had outlined. You need to
>> modify your first loop to be CCTK_LOOP3_INTBND (described in the user
>> guide, be careful when trying to use OpenMP since rho_in_shell[iradii]
>> might see contributions from different threads) so that you exclude
>> ghost zones. You also have to multiply rhop[i3D] by CarpetReduce's
>> weight function (easiest is to inherit from CarpetReduce which will
>> give you access to the grid function). You can do the Reduction all in
>> one MPI call if you'd like:
>>
>> const int op_sum = CCTK_ReductionArrayHandle("sum");
>> const int ierr = CCTK_ReduceArray(cctkGH,-1, op_sum, nradii,
>> CCTK_VARIABLE_REAL, rho_total_shell, 1/*num_dims*/,
>> 1/*num_in_arrays*/, CCTK_VARIALBE_REAL, nradii, rho_in_shell);
>>
>> or one of of the 1D ArrayToArray helper routines
>> (CCTK_ReduceLocArrayToArray1D) described in the user guide.
>>
>> Yours,
>> Roland
>>
>> - --
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