说明：  SIR（Susceptibles，Infectives，Recovered）模型来研究如天花，流感，肝炎，麻疹等治愈后均有很强的免疫力的传染病
(SIR (Susceptibles, Infectives, Recovered) model to study such as smallpox, influenza, hepatitis, measles, etc. have a strong immunity after cure of infectious diseases)