MPI_Sendrecv(3) 						      LAM/MPI							   MPI_Sendrecv(3)

NAME

       MPI_Sendrecv -  Sends and receives a message

SYNOPSIS

       #include <mpi.h>
       int MPI_Sendrecv(void *sbuf, int scount, MPI_Datatype sdtype,
	  int dest, int stag, void *rbuf, int rcount,
	  MPI_Datatype rdtype, int src, int rtag,
	  MPI_Comm comm, MPI_Status *status)

INPUT PARAMETERS

       sbuf   - initial address of send buffer (choice)
       scount - number of elements in send buffer (integer)
       sdtype - type of elements in send buffer (handle)
       dest   - rank of destination (integer)
       stag   - send tag (integer)
       rcount - number of elements in receive buffer (integer)
       rdtype - type of elements in receive buffer (handle)
       src    - rank of source (integer)
       rtag   - receive tag (integer)
       comm   - communicator (handle)

OUTPUT PARAMETERS

       rbuf   - initial address of receive buffer (choice)
       status -  status  object  (Status).   This refers to the receive operation.  Can also be the MPI constant MPI_STATUS_IGNORE , if the return
	      status is not desired.

NOTES

       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 destination 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 fol-
       lowing 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 deadlock.

NOTES FOR FORTRAN

       All  MPI  routines in Fortran (except for MPI_WTIME and MPI_WTICK ) have an additional argument 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.

ERRORS

       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  exceptions	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.
       MPI_SUCCESS
	      - No error; MPI routine completed successfully.
       MPI_ERR_COMM
	      - Invalid communicator.  A common error is to use a null communicator in a call (not even allowed in MPI_Comm_rank ).
       MPI_ERR_COUNT
	      - Invalid count argument.  Count arguments must be non-negative; a count of zero is often valid.
       MPI_ERR_TYPE
	      - Invalid datatype argument.  May be an uncommitted MPI_Datatype (see MPI_Type_commit ).
       MPI_ERR_TAG
	      - 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
	       .
       MPI_ERR_RANK
	      -  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
	       .

SEE ALSO

       MPI_Sendrecv_replace

MORE INFORMATION

       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).

       http://www.mpi-forum.org/

ACKNOWLEDGEMENTS

       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/sow-
       ing/sowing.tar.gz ), the initial formatting, and some initial text for most of the MPI-1 man pages.

LOCATION

       sendrecv.c

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