'Vector mean.
Averaging is done by converting the representation to cartesian, and
taking the mean of the x, y, and z components. The result is converted
back to the same representation as the input.
Refer to `~numpy.mean` for full documentation of the arguments, noting
that ``axis`` is the entry in the ``shape`` of the representation, and
that the ``out`` argument cannot be used.
Returns
mean : representation
Vector mean, in the same representation as that of the input.'

def mean(self, *args, **kwargs):

    self._raise_if_has_differentials(u'mean')
    return self.from_cartesian(self.to_cartesian().mean(*args, **kwargs))
