例1设A∈PmBN,则 Amn=∑∑|arl n lAIm2=∑∑ar2)2 j=1i=1 I AlIm=ma:x{a;B1≤ism1sj≤m例 1 设 A P mn ，则  = = = n j m i A m ai j 1 1 || || | | 1 2 1 1 1 2 || || ( | | ) 2  = = = n j m i A m ai j A ai j i m j n i j m =      || || max{| |} 1 1