def _largest_n_values(arr, n):
    """

    Returns the index (i.e., rows or columns) of the largest n numbers

    :param arr: a numpy array
    :type arr: ``1D ndarray``
    :param n: the largest ``n`` values to return.
    :type n: ``int``
    :return: sorted list of the ``n`` largest values in ``arr`` (ascending order).
    :rtype: ``tuple``
    """
    return tuple(sorted(arr.argsort()[-n:]))
