Man Linux: Main Page and Category List


       MPI_Gather -  Gathers together values from a group of processes


       #include <mpi.h>
       int MPI_Gather(void *sbuf, int scount, MPI_Datatype sdtype,
                      void *rbuf, int rcount, MPI_Datatype rdtype,
                      int root, MPI_Comm comm)


       sbuf   - starting address of send buffer (choice)
       scount - number of elements in send buffer (integer)
       sdtype - data type of send buffer elements (handle)
       rcount -   number   of   elements  for  any  single  receive  (integer,
              significant only at root)
       rdtype - data type of recv buffer elements (significant only  at  root)
       root   - rank of receiving process (integer)
       comm   - communicator (handle)


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


       LAM/MPI  does  not yet support invoking this function on a communicator
       that contains ranks that are non-local IMPI procs.


       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


       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.
              - No error; MPI routine completed successfully.
              - Invalid communicator.   A  common  error  is  to  use  a  null
              communicator in a call (not even allowed in MPI_Comm_rank ).
              - A collective implementation was not able to be located at run-
              time for this communicator.
              - Invalid count argument.  Count arguments must be non-negative;
              a count of zero is often valid.
              - Invalid datatype argument.  May be an uncommitted MPI_Datatype
              (see MPI_Type_commit ).
              - Invalid buffer pointer.  Usually a null buffer  where  one  is
              not valid.
              -  Invalid  root.   The  root must be specified as a rank in the
              communicator.  Ranks must be between zero and the  size  of  the
              communicator minus one.


       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).


       The LAM Team would like the thank the MPICH Team for the handy  program
       to        generate        man        pages        ("doctext"       from    ),    the     initial
       formatting, and some initial text for most of the MPI-1 man pages.