AA若AmxnD = diag(a,22,..., am),Ama?AA2则DA..0484.5矩阵的分块§4.5 矩阵的分块 1 1 2 2 . m m A A A        =         1 2 1 2 , ( , , , ), m n m m A A A D diag A           =       若 = 1 1 2 2 m n m m A A DA A           =             则 O O