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NAME

       MPI_Allgather  -   Gathers  data  from  all  tasks  and  distribute the
       combined data to all tasks

SYNOPSIS

       int MPI_Allgather(const void *sendbuf, int sendcount, MPI_Datatype sendtype,
                         void *recvbuf, int recvcount, MPI_Datatype recvtype,
                         MPI_Comm comm)

INPUT PARAMETERS

       sendbuf
              - starting address of send buffer (choice)
       sendcount
              - number of elements in send buffer (integer)
       sendtype
              - data type of send buffer elements (handle)
       recvcount
              - number of elements received from any process (integer)
       recvtype
              - data type of receive buffer elements (handle)
       comm   - communicator (handle)

OUTPUT PARAMETERS

       recvbuf
              - address of receive buffer (choice)

NOTES

       The MPI standard (1.0 and 1.1) says that

       The jth block of data sent from  each  process  is  received  by  every
       process and placed in the jth block of the buffer recvbuf .

       This is misleading; a better description is

       The  block  of  data  sent  from  the  jth process is received by every
       process and placed in the jth block of the buffer recvbuf .

       This text was suggested by Rajeev Thakur and  has  been  adopted  as  a
       clarification by the MPI Forum.

THREAD AND INTERRUPT SAFETY

       This  routine  is  thread-safe.   This  means  that this routine may be
       safely used by multiple threads without the need for any  user-provided
       thread  locks.  However, the routine is not interrupt safe.  Typically,
       this is due to the use of memory allocation routines such as malloc  or
       other  non-MPICH  runtime  routines  that are themselves not interrupt-
       safe.

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

       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.  Before the value is returned, the current MPI error
       handler is called.  By default, this error handler aborts the MPI  job.
       The  error  handler  may  be  changed with MPI_Comm_set_errhandler (for
       communicators),    MPI_File_set_errhandler     (for     files),     and
       MPI_Win_set_errhandler   (for   RMA   windows).    The   MPI-1  routine
       MPI_Errhandler_set  may  be  used  but  its  use  is  deprecated.   The
       predefined  error  handler MPI_ERRORS_RETURN may be used to cause error
       values to be returned.  Note that MPI does not guarentee  that  an  MPI
       program  can  continue past an error; however, MPI implementations will
       attempt to continue whenever possible.

       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_BUFFER
              -  Invalid  buffer  pointer.  Usually a null buffer where one is
              not valid.

LOCATION

       /tmp/gyCYfBi4J6/mpich-3.1/src/mpi/coll/allgather.c

                                   2/20/2014                  MPI_Allgather(3)



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