Linux Certif

Toute la documentation sur la certification Linux LPI

MPI_Type_indexed

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 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
 

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.

SEE ALSO

MPI_Type_create_hindexed
MPI_Type_hindexed