All the MPI_Reduce are using datatypes with the same signature (1 x
MPI_DOUBLE), so this code should not generate any MPI related errors. However,
based on the fact that in the else branch the code is summing intensity with
intensity2 (and the ice-versa), that's the place I would start investigating…
George.
PS: The result of the code you posted, is to sum on rank 0 the local intensity
with all the intensity2 of all the other nodes. With the change you propose in
the else branch you will be summing intensity on rank 0 with intensity on all
the other ranks.
On Mar 4, 2013, at 23:48 , "Jeff Squyres (jsquyres)" <jsquy...@cisco.com> wrote:
> Based on your description, it sounds like there might be something else wrong
> in your code (George's point was that you need to call all collectives with
> the same signature in all processes on the communicator, but just lipping the
> output buffer from intensity to intensity2 -- or vice versa -- shouldn't
> affect that).
>
> Perhaps try with a memory-checking debugger...?
>
>
> On Mar 4, 2013, at 5:16 PM, Andrew J Gomes <a-go...@northwestern.edu> wrote:
>
>> I have the following code which does not give the expected result:
>> if (mpi_rank!=0)
>> { MPI_Reduce(&intensity,&intensity ,1,MPI_DOUBLE,MPI_SUM,0,MPI_COMM_WORLD);
>>
>> MPI_Reduce(&intensity2,&intensity2 ,1,MPI_DOUBLE,MPI_SUM,0,MPI_COMM_WORLD); }
>> else
>> {
>> MPI_Reduce(MPI_IN_PLACE,&intensity2 ,1,MPI_DOUBLE,MPI_SUM,0,MPI_COMM_WORLD);
>> MPI_Reduce(MPI_IN_PLACE,&intensity ,1,MPI_DOUBLE,MPI_SUM,0,MPI_COMM_WORLD);}
>>
>> However if I change the the order of the else block (reduction of intensity
>> variable before intensity2 variable) to :
>> else
>> {
>> MPI_Reduce(MPI_IN_PLACE,&intensity ,1,MPI_DOUBLE,MPI_SUM,0,MPI_COMM_WORLD);
>> MPI_Reduce(MPI_IN_PLACE,&intensity2 ,1,MPI_DOUBLE,MPI_SUM,0,MPI_COMM_WORLD);}
>>
>> I get the expected result. This surprised me. Is there a reason the order of
>> the else block should match the order of the if block? Is there a more
>> robust way of implementing this type of code. Thank you
>>
>> Andrew
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>
>
> --
> Jeff Squyres
> jsquy...@cisco.com
> For corporate legal information go to:
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>
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