'Vector norm.
The norm is the standard Frobenius norm, i.e., the square root of the
sum of the squares of all components with non-angular units.
Parameters
base : instance of ``self.base_representation``
Base relative to which the differentials are defined. This is
required to calculate the physical size of the differential for
all but cartesian differentials.
Returns
norm : `astropy.units.Quantity`
Vector norm, with the same shape as the representation.'

def norm(self, base=None):

    return self.to_cartesian(base).norm()
