# MPI_Type_create_darray

## 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,

|  | int array_of_gsizes[], int array_of_distribs[],
|  | int array_of_dargs[], int array_of_psizes[],
|  | int order, MPI_Datatype oldtype, MPI_Datatype *newtype)

## Fortran Syntax

INCLUDE ’mpif.h’
MPI_TYPE_CREATE_DARRAY(SIZE, RANK, NDIMS, ARRAY_OF_GSIZES,

|  | ARRAY_OF_DISTRIBS, ARRAY_OF_DARGS, ARRAY_OF_PSIZES, ORDER, |  |
|  | OLDTYPE, NEWTYPE, IERROR) |  |
|  | INTEGER |  | SIZE, RANK, NDIMS, ARRAY_OF_GSIZES(*), ARRAY_OF_DISTRIBS(*),
|  |  | ARRAY_OF_DARGS(*), ARRAY_OF_PSIZES(*), ORDER, OLDTYPE, |
|  |  | NEWTYPE, IERROR |

## C++ Syntax

#include <mpi.h>
MPI::Datatype MPI::Datatype::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) const

## 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.

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