Check if initial values and scale as well as the new physics scale
        have been set.

def _check_initial(self):
        """Check if initial values and scale as well as the new physics scale
        have been set."""
        if self.C_in is None:
            raise Exception("You have to specify the initial conditions first.")
        if self.scale_in is None:
            raise Exception("You have to specify the initial scale first.")
        if self.scale_high is None:
            raise Exception("You have to specify the high scale first.")