MPI_Type_indexed(3OpenMPI) MPI_Type_indexed(3OpenMPI)
NAME
MPI_Type_indexed - Creates an indexed datatype.
SYNTAX
C Syntax
#include <mpi.h>
int MPI_Type_indexed(int count, int *array_of_blocklengths,
int *array_of_displacements, MPI_Datatype oldtype,
MPI_Datatype *newtype)
Fortran Syntax
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
C++ Syntax
#include <mpi.h>
Datatype Datatype::Create_indexed(int count,
const int array_of_blocklengths[],
const int array_of_displacements[]) const
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 (array of integer).
oldtype Old datatype (handle).
OUTPUT PARAMETERS
newtype New datatype (handle).
IERROR Fortran only: Error status (integer).
DESCRIPTION
The function 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 multi-
ples 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
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_create_hindexed
MPI_Type_hindexed
Open MPI 1.2 September 2006 MPI_Type_indexed(3OpenMPI)