对无阻尼多自由度振动系统的模态分析（源代码为三自由度），可通过更改质量矩阵和刚度矩阵得到自己想要的振动系统。pdf为Matlab处理震动信息的英文教程(For modal analysis of undamped multi-degree-of-freedom vibration system (source code is three degrees of freedom), the desired vibration system