MPI_Type_create_darray(3)

NAME
MPI_Type_create_darray - Creates a distributed array datatype;

SYNTAX

C Syntax
#include <mpi.h>
int MPI_Type_create_darray(int size, int rank, int ndims,
	const int array_of_gsizes[], const int array_of_distribs[],
	const int array_of_dargs[], const int array_of_psizes[],
	int order, MPI_Datatype oldtype, MPI_Datatype *newtype)

INPUT PARAMETERS

size
    Size of process group (positive integer).

rank
    Rank in process group (nonnegative integer).

ndims
    Number of array dimensions as well as process grid dimensions (positive integer).

array_of_gsizes
    Number of elements of type oldtype in each dimension of global array (array of positive integers).

array_of_distribs
    Distribution of array in each dimension (array of state).

array_of_dargs
    Distribution argument in each dimension (array of positive integers).

array_of_psizes
    Size of process grid in each dimension (array of positive integers).

order
    Array storage order flag (state).

oldtype
    Old data type (handle).

OUTPUT PARAMETERS

newtype
    New data type (handle).

IERROR
    Fortran only: Error status (integer).

DESCRIPTION

MPI_Type_create_darray can be used to generate the data types corresponding to the distribution of an ndims-dimensional array of oldtype elements onto an ndims-dimensional grid of logical processes. Unused dimensions of array_of_psizes should be set to 1. For a call to MPI_Type_create_darray to be correct, the equation

    ndims-1
  pi              array_of_psizes[i] = size
    i=0

must be satisfied. The ordering of processes in the process grid is assumed to be row-major, as in the case of virtual Cartesian process topologies in MPI-1.

Each dimension of the array can be distributed in one of three ways:

- MPI_DISTRIBUTE_BLOCK - Block distribution
- MPI_DISTRIBUTE_CYCLIC - Cyclic distribution
- MPI_DISTRIBUTE_NONE - Dimension not distributed.

The constant MPI_DISTRIBUTE_DFLT_DARG specifies a default distribution argument. The distribution argument for a dimension that is not distributed is ignored. For any dimension i in which the distribution is MPI_DISTRIBUTE_BLOCK, it erroneous to specify array_of_dargs[i] * array_of_psizes[i] < array_of_gsizes[i].

For example, the HPF layout ARRAY(CYCLIC(15)) corresponds to MPI_DISTRIBUTE_CYCLIC with a distribution argument of 15, and the HPF layout ARRAY(BLOCK) corresponds to MPI_DISTRIBUTE_BLOCK with a distribution argument of MPI_DISTRIBUTE_DFLT_DARG.

The order argument is used as in MPI_TYPE_CREATE_SUBARRAY to specify the storage order. Therefore, arrays described by this type constructor may be stored in Fortran (column-major) or C (row-major) order. Valid values for order are MPI_ORDER_FORTRAN and MPI_ORDER_C.

This routine creates a new MPI data type with a typemap defined in terms of a function called "cyclic()" (see below).

Without loss of generality, it suffices to define the typemap for the MPI_DISTRIBUTE_CYCLIC case where MPI_DISTRIBUTE_DFLT_DARG is not used.

MPI_DISTRIBUTE_BLOCK and MPI_DISTRIBUTE_NONE can be reduced to the MPI_DISTRIBUTE_CYCLIC case for dimension i as follows.

MPI_DISTRIBUTE_BLOCK with array_of_dargs[i] equal to MPI_DISTRIBUTE_DFLT_DARG is equivalent to MPI_DISTRIBUTE_CYCLIC with array_of_dargs[i] set to

   (array_of_gsizes[i] + array_of_psizes[i] - 1)/array_of_psizes[i]

If array_of_dargs[i] is not MPI_DISTRIBUTE_DFLT_DARG, then MPI_DISTRIBUTE_BLOCK and DISTRIBUTE_CYCLIC are equivalent.

MPI_DISTRIBUTE_NONE is equivalent to MPI_DISTRIBUTE_CYCLIC with array_of_dargs[i] set to array_of_gsizes[i].

Finally, MPI_DISTRIBUTE_CYCLIC with array_of_dargs[i] equal to MPI_DISTRIBUTE_DFLT_DARG is equivalent to MPI_DISTRIBUTE_CYCLIC with array_of_dargs[i] set to 1.

NOTES
For both Fortran and C arrays, the ordering of processes in the process grid is assumed to be row-major. This is consistent with the ordering used in virtual Cartesian process topologies in MPI-1. To create such virtual process topologies, or to find the coordinates of a process in the process grid, etc., users may use the corresponding functions provided in MPI-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.