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Cartesian Constructor

MPI_CART_CREATE(comm_old, ndims, dims, periods, reorder, comm_cart)
[ IN comm_old] input communicator (handle)
[ IN ndims] number of dimensions of cartesian grid (integer)
[ IN dims] integer array of size ndims specifying the number of processes in each dimension
[ IN periods] logical array of size ndims specifying whether the grid is periodic ( true) or not ( false) in each dimension
[ IN reorder] ranking may be reordered ( true) or not ( false) (logical)
[ OUT comm_cart] communicator with new cartesian topology (handle)

int MPI_Cart_create(MPI_Comm comm_old, int ndims, int *dims, int *periods, int reorder, MPI_Comm *comm_cart)

MPI_CART_CREATE(COMM_OLD, NDIMS, DIMS, PERIODS, REORDER, COMM_CART, IERROR)
INTEGER COMM_OLD, NDIMS, DIMS(*), COMM_CART, IERROR
LOGICAL PERIODS(*), REORDER

MPI_CART_CREATE returns a handle to a new communicator to which the cartesian topology information is attached. If reorder = false then the rank of each process in the new group is identical to its rank in the old group. Otherwise, the function may reorder the processes (possibly so as to choose a good embedding of the virtual topology onto the physical machine). If the total size of the cartesian grid is smaller than the size of the group of comm, then some processes are returned MPI_COMM_NULL, in analogy to MPI_COMM_SPLIT. The call is erroneous if it specifies a grid that is larger than the group size.