From aoyama@XXXXXXXX Thu Dec  7 02:43:01 2006
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Date: Thu, 07 Dec 2006 17:42:50 +0900
To: William Gropp <gropp@XXXXXXXXXXX>
From: Yukiya Aoyama <aoyama@XXXXXXXX>
Subject: Re: SEND COUNT and RECEIVE COUNT
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Hi.

Thanks for your quick answer.
I understand.

I have one comment.
In MPI-1 document, I think the following 「」 part is a little ambiguous.
It may seem  ' receive count is greater than send count '  is OK.

   MPI_ALLTOALLV  recvcounts
integer array equal to the group size specifying the number of elements
「that can be received」 from each processor.

Best Regards,

Yukiya Aoyama

At 02:30 06/12/07 -0600, you wrote:
>In point-to-point operations, it is ok to provide a larger receive
>buffer as in your example (assuming that the datatypes are the
>same).  Note that what is really important is the pair (count,
>datatype), and the receive buffer specified by that must be at least
>as large as the send buffer (with the necessary modifications for
>heterogeneity).
>
>In the collective cases, the (sendcount,datatype) must describe a
>buffer that matches the relevant (recvcount,datatype) exactly.  Note
>that if the datatypes are not the same, for example a basic type for
>a send and a vector type for a receive, the send and receive counts
>will be different.
>
>Bill
>
>
>On Dec 7, 2006, at 1:42 AM, Yukiya Aoyama wrote:
>
>>
>>
>>Hi.
>>
>>I belong to RIKEN Japan.
>>
>>I have a question about send count and recv count.
>>
>>In MPI_SEND and MPI_RECV, the following is OK.
>>   In Rank 0, MPI_SEND to Rank1, sendcount is 3
>>   In Rank 1, MPI_RECV from Rank 0  recvcount is 10
>>
>>How about Collective communication ?
>>(suppose send type and receive type are the same)
>>
>>For example, in MPI_ALLTOALLV,
>>   In Rank 0,  sendcount to Rank 1 is 3
>>   In Rank 1, recvcount from Rank 0 is 10
>>Is this specification correct?
>>
>>According to MPI-1 document Section 4,4, I think the above is wrong
>>and sendcount and recvcount must be the same.
>>
>
>

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  青山　幸也 (Yukiya Aoyama)
  理化学研究所　情報基盤センター
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