  == Matrix norm ==  Hi Quietbritishjim, thanks for the post on my talk page but it wasn't completely true what you wrote.  The article states that the max norm is not submultiplicative (hence, not a matrix norm by the definition of matrix norms).  You can show that multiplying the max norm by the dimension of the matrix makes it submultiplictive and hence an actual matrix norm (see Horn and Johnson).  I'll change it back if I don't hear back from you in a couple days.  Cheers, JDW   