MPI_Type_indexed

Creates an indexed datatype

Synopsis


#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

newtype - new datatype (handle)

Notes for Fortran

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

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

The indices are displacements, and are based on a zero origin. A common error is 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 values 1,11,.... 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)

Errors

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 last argument. Before the value is returned, the current MPI error handler is called. By default, this error handler aborts the MPI job. The error handler may be changed with MPI_Errhandler_set; the predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not guarentee that an MPI program can continue past an error.

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

Location:type_ind.c