说明：  三层框架，瑞雷阻尼。 激励是白噪声。 先计算得到理论的响应时程，理论频率，再利用响应做峰值法识别频率模态，与理论频率对比。 程序只写到了画ANPSD曲线，还需要自己写一个拾取峰值的代码。
(Three story frame, Rayleigh damping. The excitation is white noise. First, the theoretical response time history and frequency are calculated, and then the peak response method is used to identify the frequency mode, which is compared with the theoretical frequency. Later, you need to write a code to pick up the frequency corresponding to the peak value.)