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NAME

MPI_Cart_map - Returns an optimal rank for the given process in a cartesian grid

SYNOPSIS

#include <mpi.h> int MPI_Cart_map(MPI_Comm comm , int ndims , int *dims , int *periods , int *newrank );

#include <pmpi.h> int PMPI_Cart_map(MPI_Comm comm , int ndims , int *dims , int *periods , int *newrank );

#include <mpi.h> int MPI::Cartcomm::Map(int ndims , const int *dims , const bool *periods ) const;

INCLUDE 'mpif.h' MPI_CART_MAP(comm , ndims , dims , periods , newrank , ierr ) INTEGER comm , ndims , dims (*), periods (*), newrank , ierr

INPUT PARAMETERS

comm - communicator (handle)

ndims - number of dimensions (integer)

dims - dimension sizes (array)

periods - periodicity of dimensions (array of boolean)

OUTPUT PARAMETER

new_rank - optimal rank (integer).

DESCRIPTION

The MPI_Cart_map() function is used to obtain the optimal placement for the current process within a cartesian grid. Given a grid of ndims dimensions given in the dims array, together with the periodicity information in the periods array the new_rank is computed. If there are less ranks in the grid than exist in communicator comm , then some processes will receive MPI_UNDEFINED as output in new_rank . If there are more ranks in the grid than exist in the communicator, then the MPI_ERR_ARG error will be returned.

In C++, the return value is new_rank .

The communicator must be a valid one (not MPI_COMM_NULL). PMPI_Cart_map() is the profiling version of this function.

ERRORS

All MPI routines except for MPI_Wtime and MPI_Wtick return an error code. The the current MPI error handler is invoked if the return value is not MPI_SUCCESS. The default error handler aborts, but this may be changed with by using the MPI_Errhandler_set() function. The predefined error handler MPI_ERRORS_RETURN may be used to cause error values to be returned instead. Note that MPI does not guarentee that an MPI program can continue past an error. In this implementation, all errors except MPI_ERR_INTERN or MPI_ERR_OTHER should always be recoverable.

In C, the error code is passed as the return value. In FORTRAN, all functions have an parameter ierr which returns the error code. MPI C++ functions do not directly return an error code. However, C++ users may want to use the MPI::ERRORS_THROW_EXCEPTIONS handler. This will throw an MPI::Exception with the corresponding error code. To prevent exceptions from being raised from within C and Fortran code, they will see all error return values as MPI_ERR_PENDING when this handler is chosen. In this implementation, call MPI::throw_exception() to throw the correct exception if this occurs.

MPI_SUCCESS - No error;

MPI_ERR_PENDING - Pending exception;

MPI_ERR_COMM - Invalid communicator;

MPI_ERR_DIMS - Invalid dimension information;

MPI_ERR_ARG - Invalid output or periods array pointers, or grid is too large.

SEE ALSO

MPI_Cart_create (3) MPI_Cartdim_get (3) MPI_Dims_create (3) MPI_Cart_get (3)

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