.TH MPI_Graph_create 3 "11/12/2019" " " "MPI"

.SH NAME

MPI_Graph_create \-  Makes a new communicator to which topology information has been attached 

.SH SYNOPSIS

.nf

int MPI_Graph_create(MPI_Comm comm_old, int nnodes, const int indx[],

const int edges[], int reorder, MPI_Comm * comm_graph)

.fi

.SH INPUT PARAMETERS

.PD 0

.TP

.B comm_old 

- input communicator without topology (handle)

.PD 1

.PD 0

.TP

.B nnodes 

- number of nodes in graph (integer)

.PD 1

.PD 0

.TP

.B indx 

- array of integers describing node degrees (see below)

.PD 1

.PD 0

.TP

.B edges 

- array of integers describing graph edges (see below)

.PD 1

.PD 0

.TP

.B reorder 

- ranking may be reordered (true) or not (false) (logical)

.PD 1

.SH OUTPUT PARAMETERS

.PD 0

.TP

.B comm_graph 

- communicator with graph topology added (handle)

.PD 1

.SH NOTES

Each process must provide a description of the entire graph, not just the

neigbors of the calling process.

.SH ALGORITHM

We ignore the 

.I reorder

info currently.

.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.

.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_SUCCESS 

- No error; MPI routine completed successfully.

.PD 1

.PD 0

.TP

.B MPI_ERR_TOPOLOGY 

- Invalid topology.  Either there is no topology 

associated with this communicator, or it is not the correct type (e.g.,

.I MPI_CART

when expecting 

.I MPI_GRAPH

).

.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_ARG 

- Invalid argument.  Some argument is invalid and is not

identified by a specific error class (e.g., 

.I MPI_ERR_RANK

).

.PD 1