trusty (3) MPI_Type_indexed.openmpi.3.gz

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