正定矩阵 如果A是正定阵， lAll2 :max Ax12 max√XTATAx X≠0 lIxl2 xll2≤1 =√lmax (ATA)=λmax(A) 则cond2(A)=lAl2·‖A-1l2=元max(A)/min (A) 15 正定矩阵 如果 �是正定阵， � 7 ≔ max 89: �� 7 � 7 = max 8 *;< �=�=�� = �>?@ �=� = �>?@ (�) 则����7 � = � 7 ⋅ �A< 7 = �>?@ (�)/�>BC (�) 15