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Subject: Re: [OMPI users] what is MPI_IN_PLACE
From: George Bosilca (bosilca_at_[hidden])
Date: 2007-12-11 06:10:06


Neeraj,

MPI_IN_PLACE is defined by the MPI standard in order to allow the
users to specify that the input and output buffers for the collectives
are the same. Moreover, not all collectives support MPI_IN_PLACE and
for those that support it some strict rules apply. Please read the
collective section in the MPI standard to see all the restrictions.

   Thanks,
     george.

On Dec 11, 2007, at 5:56 AM, Neeraj Chourasia wrote:

> Hello everyone,
>
> While going through collective algorithms, I came across
> preprocessor directive MPI_IN_PLACE which is (void *)1. Its always
> being compared against source buffer(sbuf). My question is when
> MPI_IN_PLACE == sbuf condition would be true. As far as i
> understand, sbuf is the address of source buffer, which every node
> has to transfer to remaining nodes based on recursive doubling or
> say bruck algo. And it can never be equal to (void *)1. Any help is
> appreciated.
>
> Regards
> Neeraj
>
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