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.

依照定義 B為diagonal matrix, A屬於V對於任意的對角矩陣B tr(AB^T)=0 可看出a11~ann皆為0所以A的集合是所有的反對角矩陣感覺很不嚴謹啦XD不過大約是這樣