NAME¶
MPI_Type_create_subarray - Creates a data type describing an
n-dimensional subarray of an
n-dimensional array.
SYNTAX¶
C Syntax¶
#include <mpi.h>
int MPI_Type_create_subarray(int ndims, int array_of_sizes[], int array_of_subsizes[], int array_of_starts[], int order, MPI_Datatype oldtype, MPI_Datatype *newtype)
Fortran Syntax¶
INCLUDE 'mpif.h'
MPI_TYPE_CREATE_SUBARRAY( NDIMS, ARRAY_OF_SIZES, ARRAY_OF_SUBSIZES,
ARRAY_OF_STARTS, ORDER, OLDTYPE, NEWTYPE, IERROR)
INTEGER NDIMS, ARRAY_OF_SIZES(*), ARRAY_OF_SUBSIZES(*),
ARRAY_OF_STARTS(*), ORDER, OLDTYPE, NEWTYPE, IERROR
C++ Syntax¶
#include <mpi.h>
MPI::Datatype MPI::Datatype::Create_subarray(int ndims,
const int array_of_sizes[], const int array_of_subsizes[],
const int array_of_starts[], int order) const
- ndims
- Number of array dimensions (positive integer).
- array_of_sizes
- Number of elements of type oldtype in each dimension
of the full array (array of positive integers).
- array_of_subsizes
- Number of elements of type oldtype in each dimension
of the subarray (array of positive integers).
- array_of_starts
- Starting coordinates of the subarray in each dimension
(array of nonnegative integers).
- order
- Array storage order flag (state).
- oldtype
- Array element data type (handle).
OUTPUT PARAMETERS¶
- newtype
- New data type (handle).
- IERROR
- Fortran only: Error status (integer).
DESCRIPTION¶
The subarray type constructor creates an MPI data type describing an
n-dimensional subarray of an
n-dimensional array. The subarray
may be situated anywhere within the full array, and may be of any nonzero size
up to the size of the larger array as long as it is confined within this
array. This type constructor facilitates creating file types to access arrays
distributed in blocks among processes to a single file that contains the
global array.
This type constructor can handle arrays with an arbitrary number of dimensions
and works for both C- and Fortran-ordered matrices (that is, row-major or
column-major). Note that a C program may use Fortran order and a Fortran
program may use C order.
The
ndims parameter specifies the number of dimensions in the full data
array and gives the number of elements in
array_of_sizes,
array_of_subsizes, and
array_of_starts.
The number of elements of type
oldtype in each dimension of the
n-dimensional array and the requested subarray are specified by
array_of_sizes and
array_of_subsizes, respectively. For any
dimension
i, it is erroneous to specify
array_of_subsizes[i]
< 1 or
array_of_subsizes[i] >
array of sizes[i].
The
array_of_starts contains the starting coordinates of each dimension
of the subarray. Arrays are assumed to be indexed starting from zero. For any
dimension
i, it is erroneous to specify
array_of_starts[i] < 0
or
array_of_starts[i] > (array_of_sizes[i] - array_of_subsizes[i]).
The
order argument specifies the storage order for the subarray as well
as the full array. It must be set to one of the following:
- MPI_ORDER_C: The ordering used by C arrays, (that is, row-major order)
- MPI_ORDER_FORTRAN: The ordering used by Fortran arrays, (that is, column-major
order)
A
ndims-dimensional subarray (
newtype) with no extra padding can
be defined by the function Subarray() as follows:
newtype = Subarray(ndims, {size , size ,..., size },
0 1 ndims-1
{subsize , subsize , ..., subsize },
0 1 ndims-1
{start , start , ..., start }, oldtype)
0 1 ndims-1
Let the typemap of
oldtype have the form:
{(type , disp ), (type , disp ), ..., (type , disp )}
0 0 1 1 n-1 n-1
where type
i is a predefined MPI data type, and let
ex be the
extent of
oldtype.
The Subarray() function is defined recursively in three equations on page 72 of
the MPI-2 standard.
For an example use of MPI_Type_create_subarray in the context of I/O, see
Section 9.9.2 of the MPI-2 standard.
NOTES¶
In a Fortran program with arrays indexed starting from 1, if the starting
coordinate of a particular dimension of the subarray is
n, then the
entry in array of starts for that dimension is
n-1.
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.