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MPI_Sendrecv_replace(3) 		     LAM/MPI			  MPI_Sendrecv_replace(3)

       MPI_Sendrecv_replace -  Sends and receives using a single buffer

       #include <mpi.h>
       int MPI_Sendrecv_replace(void *buf, int count,
	   MPI_Datatype dtype, int dest, int stag,
	   int src, int rtag, MPI_Comm comm,
	   MPI_Status *status)

       count  - number of elements in send and receive buffer (integer)
       dtype  - type of elements in send and receive buffer (handle)
       dest   - rank of destination (integer)
       stag   - send message tag (integer)
       src    - rank of source (integer)
       rtag   - receive message tag (integer)
       comm   - communicator (handle)

       buf    - initial address of send and receive buffer (choice)
       status - status object (Status)

       To dispell a common misconception: src and dest do not have to be the same.  Additionally,
       a common mistake when using this function is to mismatch the tags with the source and des-
       tination ranks, which can result in deadlock.

       This  function  is  guaranteed not to deadlock in situations where pairs of blocking sends
       and receives may deadlock.  For example, the following code may deadlock if all	ranks  in
       MPI_COMM_WORLD execute it simultaneously

       int rank, size, to, from;
       MPI_Comm_rank(MPI_COMM_WORLD, &rank);
       MPI_Comm_size(MPI_COMM_WORLD, &size);
       to = (rank + 1) % size;
       from = (rank + size - 1) % size;
       MPI_Send(send_buffer, ..., to, tag, MPI_COMM_WORLD);
       MPI_Recv(recv_buffer, ..., from, tag, MPI_COMM_WORLD);

       If even one rank's MPI_Send blocks and never completes, the entire operation may deadlock.
       One alternative is to use MPI_Sendrecv in this situation because it is guaranteed  not  to

       All MPI routines in Fortran (except for MPI_WTIME and MPI_WTICK ) have an additional argu-
       ment ierr at the end of the argument list.  ierr is an integer and has the same meaning as
       the  return  value of the routine in C.	In Fortran, MPI routines are subroutines, and are
       invoked with the call statement.

       All MPI objects (e.g., MPI_Datatype , MPI_Comm ) are of type INTEGER in Fortran.

       If an error occurs in an MPI function, the current MPI error handler is called  to  handle
       it.   By default, this error handler aborts the MPI job.  The error handler may be changed
       with MPI_Errhandler_set ; the predefined error handler MPI_ERRORS_RETURN may  be  used  to
       cause  error values to be returned (in C and Fortran; this error handler is less useful in
       with the C++ MPI bindings.   The  predefined  error  handler  MPI::ERRORS_THROW_EXCEPTIONS
       should  be  used in C++ if the error value needs to be recovered).  Note that MPI does not
       guarantee that an MPI program can continue past an error.

       All MPI routines (except MPI_Wtime and MPI_Wtick ) return an error value;  C  routines  as
       the value of the function and Fortran routines in the last argument.  The C++ bindings for
       MPI do not return error values; instead, error values are communicated by throwing  excep-
       tions  of  type	MPI::Exception	(but  not by default).	Exceptions are only thrown if the
       error value is not MPI::SUCCESS

       Note that if the MPI::ERRORS_RETURN handler is set in C++, while MPI functions will return
       upon an error, there will be no way to recover what the actual error value was.
	      - No error; MPI routine completed successfully.
	      -  Invalid  communicator.   A  common error is to use a null communicator in a call
	      (not even allowed in MPI_Comm_rank ).
	      - Invalid count argument.  Count arguments must be non-negative; a count of zero is
	      often valid.
	      - Invalid datatype argument.  May be an uncommitted MPI_Datatype (see MPI_Type_com-
	      mit ).
	      - Invalid tag argument.  Tags must be non-negative; tags in a receive ( MPI_Recv	,
	      MPI_Irecv , MPI_Sendrecv , etc.)	may also be MPI_ANY_TAG
	       .  The largest tag value is available through the the attribute MPI_TAG_UB
	      -  Invalid  source or destination rank.  Ranks must be between zero and the size of
	      the  communicator  minus	one;  ranks  in  a  receive  (	MPI_Recv  ,  MPI_Irecv	,
	      MPI_Sendrecv , etc.) may also be MPI_ANY_SOURCE
	      -  Message  truncated  on receive.  The buffer size specified was too small for the
	      received message.  This is a recoverable error in the LAM/MPI implementation.
	      - This error is returned when some part of the LAM/MPI implementation is unable  to
	      acquire memory.


       For  more information, please see the official MPI Forum web site, which contains the text
       of both the MPI-1 and MPI-2 standards.  These documents contain detailed information about
       each MPI function (most of which is not duplicated in these man pages).


       The  LAM  Team  would  like the thank the MPICH Team for the handy program to generate man
       pages ("doctext" from ftp://ftp.mcs.anl.gov/pub/sowing/sowing.tar.gz ), the  initial  for-
       matting, and some initial text for most of the MPI-1 man pages.


LAM/MPI 6.5.8				    11/10/2002			  MPI_Sendrecv_replace(3)
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