MPI_Get_elements(3)                Open MPI                MPI_Get_elements(3)



NAME
       MPI_Get_elements  - Returns the number of basic elements in a data
       type.


SYNTAX
C Syntax
       #include <mpi.h>
       int MPI_Get_elements(MPI_Status *status, MPI_Datatype datatype,
            int *count)


Fortran Syntax
       INCLUDE 'mpif.h'
       MPI_GET_ELEMENTS(STATUS, DATATYPE, COUNT, IERROR)
            INTEGER   STATUS(MPI_STATUS_SIZE), DATATYPE, COUNT, IERROR


C++ Syntax
       #include <mpi.h>
       int Status::Get_elements(const Datatype& datatype) const


INPUT PARAMETERS
       status    Return status of receive operation (status).

       datatype  Datatype used by receive operation (handle).


OUTPUT PARAMETERS
       count     Number of received basic elements (integer).

       IERROR    Fortran only: Error status (integer).


DESCRIPTION
       MPI_Get_elements behaves different from MPI_Get_count, which returns
       the number of "top-level entries" received, i.e., the number of
       "copies" of type datatype. MPI_Get_count may return any integer value
       k, where 0 =< k =< count. If MPI_Get_count returns k, then the number
       of basic elements received (and the value returned by
       MPI_Get_elements) is n * k, where n is the number of basic elements in
       the type map of datatype. If the number of basic elements received is
       not a multiple of n, that is, if the receive operation has not received
       an integral number of datatype "copies," then MPI_Get_count returns the
       value MPI_UNDEFINED.

       Example: Usage of MPI_Get_count and MPI_Get_element:

         ...
         CALL MPI_TYPE_CONTIGUOUS(2, MPI_REAL, Type2, ierr)
         CALL MPI_TYPE_COMMIT(Type2, ierr)
         ...
         CALL MPI_COMM_RANK(comm, rank, ierr)
         IF(rank.EQ.0) THEN
               CALL MPI_SEND(a, 2, MPI_REAL, 1, 0, comm, ierr)
               CALL MPI_SEND(a, 3, MPI_REAL, 1, 0, comm, ierr)
         ELSE
               CALL MPI_RECV(a, 2, Type2, 0, 0, comm, stat, ierr)
               CALL MPI_GET_COUNT(stat, Type2, i, ierr)     ! returns i=1
               CALL MPI_GET_ELEMENTS(stat, Type2, i, ierr)  ! returns i=2
               CALL MPI_RECV(a, 2, Type2, 0, 0, comm, stat, ierr)
               CALL MPI_GET_COUNT(stat, Type2, i, ierr) ! returns i=MPI_UNDEFINED
               CALL MPI_GET_ELEMENTS(stat, Type2, i, ierr)  ! returns i=3
         END IF

       The function MPI_Get_elements can also be used after a probe to find
       the number of elements in the probed message. Note that the two
       functions MPI_Get_count and MPI_Get_elements return the same values
       when they are used with primitive data types.


ERRORS
       Almost all MPI routines return an error value; C routines as the value
       of the function and Fortran routines in the last argument. C++
       functions do not return errors. If the default error handler is set to
       MPI::ERRORS_THROW_EXCEPTIONS, then on error the C++ exception mechanism
       will be used to throw an MPI:Exception object.

       Before the error value is returned, the current MPI error handler is
       called. By default, this error handler aborts the MPI job, except for
       I/O function errors. The error handler may be changed with
       MPI_Comm_set_errhandler; 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.


SEE ALSO
       MPI_Get_count




1.4.1                            Jan 14, 2010              MPI_Get_elements(3)
