.TH MPI_Gatherv 3 "11/19/2001" "LAM/MPI 6.5.6" "LAM/MPI"
.SH NAME
MPI_Gatherv \-  Gathers into specified locations from all processes in a group 
.SH SYNOPSIS
.nf
#include <mpi.h>
int MPI_Gatherv(void *sbuf, int scount, MPI_Datatype sdtype,
  void *rbuf, int *rcounts, int *disps, 
  MPI_Datatype rdtype, int root, MPI_Comm comm)
.fi
.SH INPUT PARAMETERS
.PD 0
.TP
.B sendbuf 
- starting address of send buffer (choice) 
.PD 1
.PD 0
.TP
.B sendcount 
- number of elements in send buffer (integer) 
.PD 1
.PD 0
.TP
.B sendtype 
- data type of send buffer elements (handle) 
.PD 1
.PD 0
.TP
.B recvcounts 
- integer array (of length group size) 
containing the number of elements that are received from each process
(significant only at 
.I root
) 
.PD 1
.PD 0
.TP
.B displs 
- integer array (of length group size). Entry 
.I i
specifies the displacement relative to recvbuf  at
which to place the incoming data from process  
.I i
(significant only
at root) 
.PD 1
.PD 0
.TP
.B recvtype 
- data type of recv buffer elements 
(significant only at 
.I root
) (handle) 
.PD 1
.PD 0
.TP
.B root 
- rank of receiving process (integer) 
.PD 1
.PD 0
.TP
.B comm 
- communicator (handle) 
.PD 1

.SH OUTPUT PARAMETER
.PD 0
.TP
.B recvbuf 
- address of receive buffer (choice, significant only at 
.I root
) 
.PD 1

.SH USAGE WITH IMPI EXTENSIONS

LAM/MPI does not yet support invoking this function on a communicator
that contains ranks that are non-local IMPI procs.

.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.

.SH ERRORS

If an error occurs in an MPI function, the current MPI error handler
is called to handle it.  By default, this error handler aborts the
MPI job.  The error handler may be changed with 
.I MPI_Errhandler_set
;
the predefined error handler 
.I MPI_ERRORS_RETURN
may be used to cause
error values to be returned (in C and Fortran; this error handler is
less useful in with the C++ MPI bindings.  The predefined error
handler 
.I MPI::ERRORS_THROW_EXCEPTIONS
should be used in C++ if the
error value needs to be recovered).  Note that MPI does 
.I not
guarantee that an MPI program can continue past an error.

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.  The C++ bindings for MPI do not return error
values; instead, error values are communicated by throwing exceptions
of type 
.I MPI::Exception
(but not by default).  Exceptions are only
thrown if the error value is not 
.I MPI::SUCCESS
 .

Note that if the 
.I MPI::ERRORS_RETURN
handler is set in C++, while
MPI functions will return upon an error, there will be no way to
recover what the actual error value was.
.PD 0
.TP
.B MPI_SUCCESS 
- No error; MPI routine completed successfully.
.PD 1
.PD 0
.TP
.B MPI_ERR_COMM 
- Invalid communicator.  A common error is to use a
null communicator in a call (not even allowed in 
.I MPI_Comm_rank
).
.PD 1
.PD 0
.TP
.B MPI_ERR_COMM 
- Invalid communicator.  LAM/MPI does not yet support
invoking collectives on intercommunicators.
.PD 1
.PD 0
.TP
.B MPI_ERR_COMM 
- A communicator that contains some non-local IMPI
procs was used for some function which has not yet had the IMPI
extensions implemented yet.  For example, most collectives on IMPI
communicators have not been implemented yet.
.PD 1
.PD 0
.TP
.B MPI_ERR_TYPE 
- Invalid datatype argument.  May be an uncommitted
MPI_Datatype (see 
.I MPI_Type_commit
).
.PD 1
.PD 0
.TP
.B MPI_ERR_BUFFER 
- Invalid buffer pointer.  Usually a null buffer
where one is not valid.
.PD 1
.PD 0
.TP
.B MPI_ERR_ROOT 
- Invalid root.  The root must be specified as a rank
in the communicator.  Ranks must be between zero and the size of the
communicator minus one.
.PD 1
.PD 0
.TP
.B MPI_ERR_ARG 
- Invalid argument.  Some argument is invalid and is not
identified by a specific error class.  This is typically a NULL
pointer or other such error.
.PD 1

.SH MORE INFORMATION

For more information, please see the official MPI Forum web site,
which contains the text of both the MPI-1 and MPI-2 standards.  These
documents contain detailed information about each MPI function (most
of which is not duplicated in these man pages).

.I http://www.mpi-forum.org/


.SH ACKNOWLEDGEMENTS

The LAM Team would like the thank the MPICH Team for the handy program
to generate man pages ("doctext" from
.I ftp://ftp.mcs.anl.gov/pub/sowing/sowing.tar.gz
), the initial
formatting, and some initial text for most of the MPI-1 man pages.
.SH LOCATION
gatherv.c