说明：  幂法是一种计算矩阵主特征值（矩阵按模最大的特征值）及对应特征向量的迭代方法，特别适用于大型稀疏矩阵。 但是，一般幂法迭代向量v的各个不等于零的分量将随k 趋向于无穷大而使计算机溢出。因此，我们必须对某通幕法进行规范。即规范化幂法
(Power Method is a calculation of the main eigenvalue matrix (matrix according to the largest eigenvalue modulus) and the corresponding eigenvector of the iterative method, especially for large sparse matrix. However, the general power-law iteration vector v is not equal to zero all the components will be as k tends to infinity overflow of the computer. Therefore, we must pass a law to regulate screen. That is, standardized Power Method)