.\" -*- nroff -*- .\" Copyright 2013 Los Alamos National Security, LLC. All rights reserved. .\" Copyright 2010 Cisco Systems, Inc. All rights reserved. .\" Copyright 2006-2008 Sun Microsystems, Inc. .\" Copyright (c) 1996 Thinking Machines Corporation .\" $COPYRIGHT$ .TH MPI_Cart_sub 3 "Jan 31, 2017" "2.0.2" "Open MPI" .SH NAME \fBMPI_Cart_sub \fP \- Partitions a communicator into subgroups, which form lower-dimensional Cartesian subgrids. .SH SYNTAX .ft R .SH C Syntax .nf #include int MPI_Cart_sub(MPI_Comm \fIcomm\fP, const int\fI remain_dims\fP[], MPI_Comm\fI *comm_new\fP) .fi .SH Fortran Syntax .nf INCLUDE 'mpif.h' MPI_CART_SUB(\fICOMM, REMAIN_DIMS, COMM_NEW, IERROR\fP) INTEGER \fICOMM, COMM_NEW, IERROR\fP LOGICAL \fIREMAIN_DIMS\fP(*) .fi .SH C++ Syntax .nf #include Cartcomm Cartcomm::Sub(const bool \fIremain_dims\fP[]) const .fi .SH INPUT PARAMETERS .ft R .TP 1i comm Communicator with Cartesian structure (handle). .TP 1i remain_dims The ith entry of remain_dims specifies whether the ith dimension is kept in the subgrid (true) or is dropped (false) (logical vector). .SH OUTPUT PARAMETERS .ft R .TP 1i comm_new Communicator containing the subgrid that includes the calling process (handle). .ft R .TP 1i IERROR Fortran only: Error status (integer). .SH DESCRIPTION .ft R If a Cartesian topology has been created with MPI_Cart_create, the function MPI_Cart_sub can be used to partition the communicator group into subgroups that form lower-dimensional Cartesian subgrids, and to build for each subgroup a communicator with the associated subgrid Cartesian topology. (This function is closely related to MPI_Comm_split.) .sp \fBExample:\fP Assume that MPI_Cart_create( \&..., comm) has defined a (2 x 3 x 4) grid. Let remain_dims = (true, false, true). Then a call to .sp .nf MPI_Cart_sub(comm, remain_dims, comm_new) .fi .sp will create three communicators, each with eight processes in a 2 x 4 Cartesian topology. If remain_dims = (false, false, true) then the call to MPI_Cart_sub(comm, remain_dims, comm_new) will create six nonoverlapping communicators, each with four processes, in a one-dimensional Cartesian topology. .SH ERRORS Almost all MPI routines return an error value; C routines as the value of the function and Fortran routines in the last argument. C++ functions do not return errors. If the default error handler is set to MPI::ERRORS_THROW_EXCEPTIONS, then on error the C++ exception mechanism will be used to throw an MPI::Exception object. .sp Before the error value is returned, the current MPI error handler is called. By default, this error handler aborts the MPI job, except for I/O function errors. The error handler may be changed with MPI_Comm_set_errhandler; the predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned. Note that MPI does not guarantee that an MPI program can continue past an error. .SH SEE ALSO .ft R .sp .nf MPI_Cart_create MPI_Comm_split