Let V be the vector space of all nxn matrices with the inner product
<A,B> = tr(AB^T) .Find the orthogonal conplement of the subspace of diagonal
matrics.

依照定义 B为diagonal matrix, A属于V对于任意的对角矩阵B tr(AB^T)=0 可看出a11~ann皆为0所以A的集合是所有的反对角矩阵感觉很不严谨啦XD不过大约是这样