oracular (3) MPI_Get_elements.openmpi.3.gz

NAME

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

SYNTAX

C Syntax

       #include <mpi.h>
       int MPI_Get_elements(const MPI_Status *status, MPI_Datatype datatype,
            int *count)
       int MPI_Get_elements_x(const MPI_Status *status, MPI_Datatype datatype,
            MPI_Count *count)

Fortran Syntax

       USE MPI
       ! or the older form: INCLUDE 'mpif.h'
       MPI_GET_ELEMENTS(STATUS, DATATYPE, COUNT, IERROR)
            INTEGER   STATUS(MPI_STATUS_SIZE), DATATYPE, COUNT, IERROR
       MPI_GET_ELEMENTS_X(STATUS, DATATYPE, COUNT, IERROR)
            INTEGER   STATUS(MPI_STATUS_SIZE), DATATYPE
               INTEGER(KIND=MPI_COUNT_KIND) COUNT
               INTEGER IERROR

Fortran 2008 Syntax

       USE mpi_f08
       MPI_Get_elements(status, datatype, count, ierror)
            TYPE(MPI_Status), INTENT(IN) :: status
            TYPE(MPI_Datatype), INTENT(IN) :: datatype
            INTEGER, INTENT(OUT) :: count
            INTEGER, OPTIONAL, INTENT(OUT) :: ierror
       MPI_Get_elements_x(status, datatype, count, ierror)
            TYPE(MPI_Status), INTENT(IN) :: status
            TYPE(MPI_Datatype), INTENT(IN) :: datatype
            INTEGER(KIND = MPI_COUNT_KIND), INTENT(OUT) :: count
            INTEGER, OPTIONAL, INTENT(OUT) :: 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  and MPI_Get_elements_x behave 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 and MPI_Get_elements_x) 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. For both functions, if the count parameter
       cannot express the value to be returned (e.g., if the parameter is too small to hold the  output  value),
       it is set to 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.

FORTRAN 77 NOTES

       The MPI standard prescribes portable Fortran syntax for the COUNT argument of MPI_Get_elements_x only for
       Fortran 90. FORTRAN 77 users may use the non-portable syntax

            INTEGER*MPI_COUNT_KIND COUNT

       where MPI_COUNT_KIND is a constant defined in mpif.h and gives the length  of  the  declared  integer  in
       bytes.

SEE ALSO

       MPI_Get_count