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MPI_Type_lb.3.rst

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MPI_Type_lb

:ref:`MPI_Type_lb` - Returns the lower bound of a data type -- |deprecated_favor| :ref:`MPI_Type_get_extent`.

SYNTAX

C Syntax

#include <mpi.h>

int MPI_Type_lb(MPI_Datatype datatype, MPI_Aint *displacement)

Fortran Syntax

USE MPI
! or the older form: INCLUDE 'mpif.h'

MPI_TYPE_LB(DATATYPE, DISPLACEMENT, IERROR)
     INTEGER DATATYPE, DISPLACEMENT, IERROR

INPUT PARAMETER

  • datatype: Datatype (handle).

OUTPUT PARAMETERS

  • displacement: Displacement of lower bound from origin, in bytes (integer).
  • ierror: Fortran only: Error status (integer).

DESCRIPTION

Note that use of this routine is deprecated as of MPI-2. Please use :ref:`MPI_Type_get_extent` instead.

:ref:`MPI_Type_lb` returns the lower bound of a data type. This may differ from zero if the type was constructed using MPI_LB.

The "pseudo-datatypes," MPI_LB and MPI_UB, can be used, respectively, to mark the lower bound (or the upper bound) of a datatype. These pseudo-datatypes occupy no space (extent (MPI_LB) = extent (MPI_UB) =0. They do not affect the size or count of a datatype, and do not affect the context of a message created with this datatype. However, they do affect the definition of the extent of a datatype and, therefore, affect the outcome of a replication of this datatype by a datatype constructor.

In general, if

Typemap = {(type0, disp0), ..., (type(n-1), disp(n-1)}

then the lower bound of Typemap is defined to be

              (min(j) disp(j)                          if no entry has
lb(Typemap) = (                                        basic type lb
              (min(j) {disp(j) such that type(j) = lb} otherwise

Similarly, the upper bound of Typemap is defined to be

                  (max(j) disp(j) + sizeof((type(j)) + e   if no entry has
    ub(Typemap) = (                                        basic type ub
                  (max(j) {disp(j) such that type(j) = ub} otherwise

Then

    extent(Typemap) = ub(Typemap) - lb(Typemap)

If type(i) requires alignment to a byte address that is a multiple of k(i), then e is the least nonnegative increment needed to round extent(Typemap) to the next multiple of max(i) k(i).

ERRORS

.. seealso::
   * :ref:`MPI_Type_get_extent`