NAME¶
MPI_Dims_create - Creates a division of processors in a Cartesian grid.
SYNTAX¶
C Syntax¶
#include <mpi.h>
int MPI_Dims_create(int nnodes, int ndims, int *dims)
Fortran Syntax¶
INCLUDE 'mpif.h'
MPI_DIMS_CREATE( NNODES, NDIMS, DIMS, IERROR)
INTEGER NNODES, NDIMS, DIMS(*), IERROR
C++ Syntax¶
#include <mpi.h>
void Compute_dims(int nnodes, int ndims, int dims[])
- nnodes
- Number of nodes in a grid (integer).
- ndims
- Number of Cartesian dimensions (integer).
IN/OUT PARAMETER¶
- dims
- Integer array of size ndims specifying the number of nodes
in each dimension.
OUTPUT PARAMETER¶
- IERROR
- Fortran only: Error status (integer).
DESCRIPTION¶
For Cartesian topologies, the function MPI_Dims_create helps the user select a
balanced distribution of processes per coordinate direction, depending on the
number of processes in the group to be balanced and optional constraints that
can be specified by the user. One use is to partition all the processes (the
size of MPI_COMM_WORLD's group) into an n-dimensional topology.
The entries in the array
dims are set to describe a Cartesian grid with
ndims dimensions and a total of
nnodes nodes. The dimensions are
set to be as close to each other as possible, using an appropriate
divisibility algorithm. The caller may further constrain the operation of this
routine by specifying elements of array dims. If dims[i] is set to a positive
number, the routine will not modify the number of nodes in dimension i; only
those entries where dims[i] = 0 are modified by the call.
Negative input values of dims[i] are erroneous. An error will occur if nnodes is
not a multiple of ((pi) over (i, dims[i] != 0)) dims[i].
For dims[i] set by the call, dims[i] will be ordered in nonincreasing order.
Array dims is suitable for use as input to routine MPI_Cart_create.
MPI_Dims_create is local.
Example:
dims
before dims
call function call on return
-----------------------------------------------------
(0,0) MPI_Dims_create(6, 2, dims) (3,2)
(0,0) MPI_Dims_create(7, 2, dims) (7,1)
(0,3,0) MPI_Dims_create(6, 3, dims) (2,3,1)
(0,3,0) MPI_Dims_create(7, 3, dims) erroneous call
------------------------------------------------------
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.
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.
