def gradient(self):
        """
        Return a view on the gradient, which is in the same shape as this parameter is.
        Note: this is not the real gradient array, it is just a view on it.

        To work on the real gradient array use: self.full_gradient
        """
        if getattr(self, '_gradient_array_', None) is None:
            self._gradient_array_ = np.empty(self._realshape_, dtype=np.float64)
        return self._gradient_array_