show equations used for the EOS

def print_equations(self):
        """
        show equations used for the EOS
        """
        print("P_static: ", self.eqn_st)
        print("P_thermal: ", self.eqn_th)
        print("P_anharmonic: ", self.eqn_anh)
        print("P_electronic: ", self.eqn_el)