NAME

       MPI_Sendrecv_replace -  Sends and receives using a single buffer

SYNOPSIS

       #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)

INPUT PARAMETERS

       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)

OUTPUT PARAMETERS

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

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 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
       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 .

       MPI_ERR_TRUNCATE
              - 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.
       MPI_ERR_OTHER
              -  This error is returned when some part of the LAM/MPI implementation is unable to
              acquire memory.

SEE ALSO

       MPI_Sendrecv

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

LOCATION

       sendrecvrep.c