NAME

       MPI_Iallreduce  -  Combines values from all processes and distributes the result back to all processes in
       a nonblocking way

SYNOPSIS

       int MPI_Iallreduce(const void *sendbuf, void *recvbuf, int count,
       MPI_Datatype datatype, MPI_Op op, MPI_Comm comm,
       MPI_Request *request)

       int MPI_Iallreduce_c(const void *sendbuf, void *recvbuf, MPI_Count count,
       MPI_Datatype datatype, MPI_Op op, MPI_Comm comm,
       MPI_Request *request)

INPUT PARAMETERS

       sendbuf
              - starting address of send buffer (choice)
       count  - number of elements in send buffer (non-negative integer)
       datatype
              - data type of elements of send buffer (handle)
       op     - operation (handle)
       comm   - communicator (handle)

OUTPUT PARAMETERS

       recvbuf
              - starting address of receive buffer (choice)
       request
              - communication request (handle)

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_ARG
              - Invalid argument.  Some argument is invalid and is not identified  by  a  specific  error  class
              (e.g., MPI_ERR_RANK ).
       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_OP
              - Invalid operation.  MPI operations (objects  of  type  MPI_Op  )  must  either  be  one  of  the
              predefined operations (e.g., MPI_SUM ) or created with MPI_Op_create .

       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.

                                                    2/9/2024                                   MPI_Iallreduce(3)