TODO: Doc strings

def dlogpdf_dtheta(self, f, y, Y_metadata=None):
        """
        TODO: Doc strings
        """
        if self.size > 0:
            if self.not_block_really:
                raise NotImplementedError("Need to make a decorator for this!")
            if isinstance(self.gp_link, link_functions.Identity):
                return self.dlogpdf_link_dtheta(f, y, Y_metadata=Y_metadata)
            else:
                inv_link_f = self.gp_link.transf(f)
                return self.dlogpdf_link_dtheta(inv_link_f, y, Y_metadata=Y_metadata)
        else:
            # There are no parameters so return an empty array for derivatives
            return np.zeros((0, f.shape[0], f.shape[1]))