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 (non-negative integer)
       sendtype
              - data type of send buffer elements (handle)
       recvcount
              - number of elements received from any process (non-negative 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  guarantee that an MPI program can continue past an
       error; however, MPI implementations will attempt to continue whenever possible.

       MPI_SUCCESS
              - No error; MPI routine completed successfully.

       MPI_ERR_BUFFER
              - Invalid buffer pointer.  Usually a null buffer where one is not valid.
       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.  Additionally, this error can occur if an  uncommitted
              MPI_Datatype (see MPI_Type_commit ) is used in a communication call.
       MPI_ERR_OTHER
              - Other error; use MPI_Error_string to get more information about this error code.

                                            2/22/2022                            MPI_Allgather(3)