def norm(x, ord=None):
    """
    Returns the vector norm of *x*, if that is defined.

    The norm returned depends on the *ord* parameter, as in SciPy.

    :param: ord : {1, 2, inf, 'fro', None}
        Order of the norm.
        *inf* means NumPy's :class:`inf` object.
        *'fro'* means the string 'fro', and denotes the Frobenius norm.
        If *None* and self is a Matrix instance, then assumes 'fro'.
    """
    return x.norm(ord)