对于一个实对称矩阵A，QR算法采用的是Householder矩阵，先将A约化为对称三对角矩阵，然后再用QR法求对称三角矩阵的特征值和特征向量- for A real symmetric matrix A, QR algorithm USES is the Householder matrix, the first A symmetrical about into three diagonal matrix, and then use QR method for the symmetric triangle matrix eigenvalues and eigenvectors