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, 特别是用于大型稀疏矩阵。
(The power method is a method of calculating the matrix eigenvalue (matrix largest characteristic value) and the iterative method of the corresponding feature vector, particularly for large sparse matrix.)