Creates an indexed datatype


#include "mpi.h"
int MPI_Type_indexed( count, blocklens, indices, old_type, newtype )
int           count;
int        blocklens[];
int        indices[];
MPI_Datatype  old_type;
MPI_Datatype *newtype;

Input Parameters

count number of blocks -- also number of entries in indices and blocklens
blocklens number of elements in each block (array of nonnegative integers)
indices displacement of each block in multiples of old_type (array of integers)
old_type old datatype (handle)

Output Parameter

new datatype (handle)

Notes for Fortran

All MPI routines in Fortran (except for MPI_WTIME and MPI_WTICK) havean additional argument ierr at the end of the argument list. ierris an integer and has the same meaning as the return value of the routinein C. In Fortran, MPI routines are subroutines, and are invoked with thecall statement.

All MPI objects (e.g., MPI_Datatype, MPI_Comm) are of type INTEGERin Fortran.

The indices are displacements, and are based on a zero origin. A common erroris to do something like to following

    integer a(100)
    integer blens(10), indices(10)
    do i=1,10
         blens(i)   = 1
10       indices(i) = 1 + (i-1)*10
    call MPI_TYPE_INDEXED(10,blens,indices,MPI_INTEGER,newtype,ierr)
    call MPI_TYPE_COMMIT(newtype,ierr)
    call MPI_SEND(a,1,newtype,...)
expecting this to send a(1),a(11),... because the indices have values1,11,.... Because these are displacements from the beginning of a, it actually sends a(1+1),a(1+11),....

If you wish to consider the displacements as indices into a Fortran array, consider declaring the Fortran array with a zero origin

    integer a(0:99)


All MPI routines (except MPI_Wtime and MPI_Wtick) return an error value; C routines as the value of the function and Fortran routines in the lastargument. Before the value is returned, the current MPI error handler iscalled. By default, this error handler aborts the MPI job. The error handlermay be changed with MPI_Errhandler_set; the predefined error handlerMPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not guarentee that an MPI program can continue pastan error.

Invalid count argument. Count arguments must be non-negative; a count of zero is often valid.
Invalid datatype argument. May be an uncommitted MPI_Datatype (see MPI_Type_commit).
Invalid argument. Some argument is invalid and is not identified by a specific error class (e.g., MPI_ERR_RANK).
This error is returned when some part of the MPICH implementation is unable to acquire memory.