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Subject: Re: [OMPI users] MPI_SCAN
From: Rohan Deshpande (rohand87_at_[hidden])
Date: 2012-05-19 13:36:43


Hi jeffy,

Thanks for your reply.

I am not understanding how MPI_Reduce would be useful.

Say I have 3 processes and each process has array [1,2,3,4]

When each process calculates the prefix sum using cuda each process will
have array as [1,3,6,10]

so if I use MPI_Reduce to gather results it returns me sum as 30.

but the original array is [1,2,3,4,1,2,3,4,1,2,3,4] and the prefix sum of
this array should be

[1,3,6,10,11,13,16,20,21,23,26,30]

Is my understanding wrong somewhere?

On Fri, May 18, 2012 at 7:05 AM, Jeff Squyres <jsquyres_at_[hidden]> wrote:

> You probably want MPI_Reduce, instead.
>
> http://www.open-mpi.org/doc/v1.6/man3/MPI_Reduce.3.php
>
>
> On May 15, 2012, at 11:27 PM, Rohan Deshpande wrote:
>
> > I am performing Prefix scan operation on cluster
> >
> > I have 3 MPI tasks and master task is responsible for distributing the
> data
> >
> > Now, each task calculates sum of its own part of array using GPUs and
> returns the results to master task.
> >
> > Master task also calculates its own part of array using GPU.
> >
> > When each task returns its result (which would be array) master task
> needs to combine all the results to get the final result.
> >
> > Can I use MPI_SCAN to combine the results?
> >
> >
> >
> >
> >
> > _______________________________________________
> > users mailing list
> > users_at_[hidden]
> > http://www.open-mpi.org/mailman/listinfo.cgi/users
>
>
> --
> Jeff Squyres
> jsquyres_at_[hidden]
> For corporate legal information go to:
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>
>
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>

-- 
Best Regards,
ROHAN DESHPANDE