MPI_Type_indexed.3.rst

MPI_Type_indexed

:ref:`MPI_Type_indexed`, :ref:`MPI_Type_create_hindexed` - Creates an indexed datatype.

SYNTAX

C Syntax

#include <mpi.h>

int MPI_Type_indexed(int count, const int array_of_blocklengths[],
     const int array_of_displacements[], MPI_Datatype oldtype,
     MPI_Datatype *newtype)

int MPI_Type_create_hindexed(int count,
     const int array_of_blocklengths[],
     const MPI_Aint array_of_displacements[], MPI_Datatype oldtype,
     MPI_Datatype *newtype)

Fortran Syntax

USE MPI
! or the older form: INCLUDE 'mpif.h'
MPI_TYPE_INDEXED(COUNT, ARRAY_OF_BLOCKLENGTHS,
             ARRAY_OF_DISPLACEMENTS, OLDTYPE, NEWTYPE, IERROR)
     INTEGER COUNT, ARRAY_OF_BLOCKLENGTHS(*)
     INTEGER ARRAY_OF_DISPLACEMENTS(*), OLDTYPE, NEWTYPE
     INTEGER IERROR

MPI_TYPE_CREATE_HINDEXED(COUNT, ARRAY_OF_BLOCKLENGTHS,
             ARRAY_OF_DISPLACEMENTS, OLDTYPE, NEWTYPE, IERROR)
     INTEGER COUNT, ARRAY_OF_BLOCKLENGTHS(*)
     INTEGER OLDTYPE, NEWTYPE
     INTEGER(KIND=MPI_ADDRESS_KIND) ARRAY_OF_DISPLACEMENTS(*)
     INTEGER IERROR

Fortran 2008 Syntax

USE mpi_f08
MPI_Type_indexed(count, array_of_blocklengths, array_of_displacements,
             oldtype, newtype, ierror)
     INTEGER, INTENT(IN) :: count, array_of_blocklengths(count),
     array_of_displacements(count)
     TYPE(MPI_Datatype), INTENT(IN) :: oldtype
     TYPE(MPI_Datatype), INTENT(OUT) :: newtype
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror

MPI_Type_create_hindexed(count, array_of_blocklengths,
             array_of_displacements, oldtype, newtype, ierror)
     INTEGER, INTENT(IN) :: count, array_of_blocklengths(count)
     INTEGER(KIND=MPI_ADDRESS_KIND), INTENT(IN) ::
     array_of_displacements(count)
     TYPE(MPI_Datatype), INTENT(IN) :: oldtype
     TYPE(MPI_Datatype), INTENT(OUT) :: newtype
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror

INPUT PARAMETERS

• count: Number of blocks -- also number of entries in array_of_displacements and array_of_blocklengths (nonnegative integer).
• array_of_blocklengths: Number of elements per block (array of nonnegative integers).
• array_of_displacements: Displacement for each block, in multiples of oldtype extent for MPI_Type_indexed and bytes for MPI_Type_create_hindexed (array of integer for MPI_TYPE_INDEXED, array of MPI_Aint for MPI_TYPE_CREATE_HINDEXED).
• oldtype: Old datatype (handle).

OUTPUT PARAMETERS

• newtype: New datatype (handle).
• ierror: Fortran only: Error status (integer).

DESCRIPTION

The function :ref:`MPI_Type_indexed` allows replication of an old datatype into a sequence of blocks (each block is a concatenation of the old datatype), where each block can contain a different number of copies and have a different displacement. All block displacements are multiples of the old data type's extent.

Example: Let oldtype have type map {(double, 0), (char, 8)}, with extent 16. Let B = (3, 1) and let D = (4, 0). A call to MPI_Type_indexed(2, B, D, oldtype, newtype) returns a datatype with type map

{(double, 64), (char, 72), (double, 80), (char, 88),
(double, 96), (char, 104),
(double, 0), (char, 8)}

That is, three copies of the old type starting at displacement 4 x 16 = 64, and one copy starting at displacement 0.

In general, assume that oldtype has type map

{(type(0), disp(0)), ..., (type(n-1), disp(n-1))},

with extent ex. Let B be the array_of_blocklength argument and D be the array_of_displacements argument. The newly created datatype has

n x S ^count-1
    i = 0           B[i]  entries:

    {(type(0), disp(0) + D[0]* ex), ...,
    (type(n-1), disp(n-1) + D[0]* ex), ...,
    (type(0), disp(0) + (D[0] + B[0]-1)* ex), ...,
    (type(n-1), disp(n-1) + (D[0]+ B[0]-1)* ex), ...,
    (type(0), disp(0) + D[count-1]* ex), ...,
    (type(n-1), disp(n-1) + D[count-1]* ex), ...,
    (type(0), disp(0) +  (D[count-1] + B[count-1] -1)* ex), ...,
    (type(n-1), disp(n-1) + (D[count-1] + B[count-1] -1)* ex)}

A call to MPI_Type_vector(count, blocklength, stride, oldtype, newtype) is equivalent to a call to MPI_Type_indexed(count, B, D, oldtype, newtype) where

    D[j] = j * stride, j = 0,..., count-1

and

    B[j] = blocklength, j = 0, .., count-1

The function :ref:`MPI_Type_create_hindexed` is identical to :ref:`MPI_Type_indexed`, except that block displacements in array_of_displacements are specified in bytes, rather than in multiples of the oldtype extent.

ERRORS

.. seealso::
   * :ref:`MPI_Type_hindexed`