File: MPI_Bcast.3

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.TH MPI_Bcast 3 "1/6/1997" " " "MPI"
.SH NAME
MPI_Bcast \-  Broadcasts a message from the process with rank "root" to all other processes of the group.  
.SH SYNOPSIS
.nf
#include "mpi.h"
int MPI_Bcast ( buffer, count, datatype, root, comm )
void             *buffer;
int               count;
MPI_Datatype      datatype;
int               root;
MPI_Comm          comm;
.fi
.SH INPUT/OUTPUT PARAMETERS
.PD 0
.TP
.B buffer 
- starting address of buffer (choice) 
.PD 1
.PD 0
.TP
.B count 
- number of entries in buffer (integer) 
.PD 1
.PD 0
.TP
.B datatype 
- data type of buffer (handle) 
.PD 1
.PD 0
.TP
.B root 
- rank of broadcast root (integer) 
.PD 1
.PD 0
.TP
.B comm 
- communicator (handle) 
.PD 1

.SH ALGORITHM
If the underlying device does not take responsibility, this function
uses a tree-like algorithm to broadcast the message to blocks of
processes.  A linear algorithm is then used to broadcast the message
from the first process in a block to all other processes.
.I MPIR_BCAST_BLOCK_SIZE
determines the size of blocks.  If this is set
to 1, then this function is equivalent to using a pure tree algorithm.
If it is set to the size of the group or greater, it is a pure linear
algorithm.  The value should be adjusted to determine the most
efficient value on different machines.

.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

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_Errhandler_set
; 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.

.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_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.  May be an uncommitted 
.PD 1
MPI_Datatype (see 
.I MPI_Type_commit
).
.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
.SH LOCATION
bcast.c