manpagez: man pages & more
man MPI_Reduce(3)
Home | html | info | man
MPI_Reduce(3)                         MPI                        MPI_Reduce(3)




NAME

       MPI_Reduce -  Reduces values on all processes to a single value


SYNOPSIS

       int MPI_Reduce(const void *sendbuf, void *recvbuf, int count, MPI_Datatype datatype,
       MPI_Op op, int root, MPI_Comm comm)


INPUT PARAMETERS

       sendbuf
              - address of send buffer (choice)
       count  - number of elements in send buffer (integer)
       datatype
              - data type of elements of send buffer (handle)
       op     - reduce operation (handle)
       root   - rank of root process (integer)
       comm   - communicator (handle)



OUTPUT PARAMETERS

       recvbuf
              - address of receive buffer (choice, significant only at root )



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.



NOTES ON COLLECTIVE OPERATIONS

       The  reduction functions ( MPI_Op ) do not return an error value.  As a
       result, if the functions detect an error, all they  can  do  is  either
       call  MPI_Abort  or silently skip the problem.  Thus, if you change the
       error handler from MPI_ERRORS_ARE_FATAL to something else, for example,
       MPI_ERRORS_RETURN , then no error may be indicated.

       The  reason  for  this is the performance problems in ensuring that all
       collective routines return the same error value.



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 com-
       municators),      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 prede-
       fined 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_SUCCESS
              - No error; MPI routine completed successfully.
       MPI_ERR_COMM
              -  Invalid communicator.  A common error is to use a null commu-
              nicator 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_BUFFER
              -  Invalid  buffer  pointer.  Usually a null buffer where one is
              not valid.
       MPI_ERR_BUFFER
              - This error class is associcated with an error code that  indi-
              cates  that  two  buffer  arguments  are  aliased ; that is, the
              describe overlapping storage (often  the  exact  same  storage).
              This  is prohibited in MPI (because it is prohibited by the For-
              tran standard, and rather than have a separate case  for  C  and
              Fortran, the MPI Forum adopted the more restrictive requirements
              of Fortran).




                                  11/12/2019                     MPI_Reduce(3)

mpi 3.3.2 - Generated Tue Nov 19 19:01:29 CST 2019
© manpagez.com 2000-2020
Individual documents may contain additional copyright information.