MPI_Type_lb(3) Open MPI MPI_Type_lb(3)
NAME
MPI_Type_lb - Returns the lower bound of a data type -- use of this
routine is deprecated.
SYNTAX
C Syntax
#include <mpi.h>
int MPI_Type_lb(MPI_Datatype datatype, MPI_Aint *displacement)
Fortran Syntax
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
MPI_Type_get_extent instead.
This deprecated routine is not available in C++.
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, af-
fect the outcome of a replication of this datatype by a datatype con-
structor.
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 ex-
tent(Typemap) to the next multiple of max(i) k(i).
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++ func-
tions 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_Type_get_extent
4.1.2 Nov 24, 2021 MPI_Type_lb(3)
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