.TH MPI_Type_indexed 3 "11/12/2019" " " "MPI"
.SH NAME
MPI_Type_indexed \-  Creates an indexed datatype 
.SH SYNOPSIS
.nf
int MPI_Type_indexed(int count,
const int *array_of_blocklengths,
const int *array_of_displacements,
MPI_Datatype oldtype, MPI_Datatype * newtype)
.fi
.SH INPUT PARAMETERS
.PD 0
.TP
.B count 
- number of blocks -- also number of entries in array_of_displacements and array_of_blocklengths
.PD 1
.PD 0
.TP
.B array_of_blocklengths 
- number of elements in each block (array of nonnegative integers)
.PD 1
.PD 0
.TP
.B array_of_displacements 
- displacement of each block in multiples of oldtype (array of
integers)
.PD 1
.PD 0
.TP
.B oldtype 
- old datatype (handle)
.PD 1

.SH OUTPUT PARAMETERS
.PD 0
.TP
.B newtype 
- new datatype (handle)
.PD 1

.SH THREAD AND INTERRUPT SAFETY

This routine is thread-safe.  This means that this routine may be
safely used by multiple threads without the need for any user-provided
thread locks.  However, the routine is not interrupt safe.  Typically,
this is due to the use of memory allocation routines such as 
.I malloc
or other non-MPICH runtime routines that are themselves not interrupt-safe.

.SH NOTES FOR FORTRAN
All MPI routines in Fortran (except for 
.I MPI_WTIME
and 
.I MPI_WTICK
) have
an additional argument 
.I ierr
at the end of the argument list.  
.I 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
.I call
statement.

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

The array_of_displacements are displacements, and are based on a zero origin.  A common error
is to do something like to following
.nf
integer a(100)
integer array_of_blocklengths(10), array_of_displacements(10)
do i=1,10
array_of_blocklengths(i)   = 1
10       array_of_displacements(i) = 1 + (i-1)*10
call MPI_TYPE_INDEXED(10,array_of_blocklengths,array_of_displacements,MPI_INTEGER,newtype,ierr)
call MPI_TYPE_COMMIT(newtype,ierr)
call MPI_SEND(a,1,newtype,...)
.fi

expecting this to send "a(1),a(11),..." because the array_of_displacements have values
"1,11,...".   Because these are 
.B displacements
from the beginning of "a",
it actually sends "a(1+1),a(1+11),...".

If you wish to consider the displacements as array_of_displacements into a Fortran array,
consider declaring the Fortran array with a zero origin
.nf
integer a(0:99)
.fi


.SH ERRORS

All MPI routines (except 
.I MPI_Wtime
and 
.I 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 
.I MPI_Comm_set_errhandler
(for communicators),
.I MPI_File_set_errhandler
(for files), and 
.I MPI_Win_set_errhandler
(for
RMA windows).  The MPI-1 routine 
.I MPI_Errhandler_set
may be used but
its use is deprecated.  The predefined error handler
.I MPI_ERRORS_RETURN
may be used to cause error values to be returned.
Note that MPI does 
.B not
guarentee that an MPI program can continue past
an error; however, MPI implementations will attempt to continue whenever
possible.

.PD 0
.TP
.B MPI_ERR_COUNT 
- Invalid count argument.  Count arguments must be 
non-negative; a count of zero is often valid.
.PD 1
.PD 0
.TP
.B MPI_ERR_TYPE 
- Invalid datatype argument.  Additionally, this error can
occur if an uncommitted MPI_Datatype (see 
.I MPI_Type_commit
) is used
in a communication call.
.PD 1
.PD 0
.TP
.B MPI_ERR_ARG 
- Invalid argument.  Some argument is invalid and is not
identified by a specific error class (e.g., 
.I MPI_ERR_RANK
).
.PD 1
.PD 0
.TP
.B MPI_ERR_INTERN 
- This error is returned when some part of the MPICH 
implementation is unable to acquire memory.  
.PD 1