中文说明：该函数用逆迭代法求解广义特征值问题的第一阶特征值！通常在matlab中可以利用自带函数eigs（）求解模态问题，但是有时K，M矩阵较差，有许多接近0的元素，求解不一定能得到有效解，可基于有限元的思想采用逆迭代法和子空间法解决。子空间法还在研究中
English Description：
The function inverse iteration method for solving the generalized eigenvalue problem for first-order eigenvalue! In MATLAB, you can usually bring their own function eigs () problem solving modal, but sometimes less K,M matrix, there are many elements close to 0, solve may not be effective solutions, based on finite element inverse iteration method and space law. Subspace methods in research