:ref:`MPI_Type_lb` |mdash| Returns the lower bound of a data type |mdash| |deprecated_favor| :ref:`MPI_Type_get_extent`.
#include <mpi.h>
int MPI_Type_lb(MPI_Datatype datatype, MPI_Aint *displacement)
USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_TYPE_LB(DATATYPE, DISPLACEMENT, IERROR)
INTEGER DATATYPE, DISPLACEMENT, IERROR
datatype
: Datatype (handle).
displacement
: Displacement of lower bound from origin, in bytes (integer).ierror
: Fortran only: Error status (integer).
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).
.. seealso::
* :ref:`MPI_Type_get_extent`