On 8/19/2013 12:34 AM, James Dow Allen wrote: > Let > ( A B 0 ) > ( 0 A B ) > ( B 0 A ) > be a 3Nx3N real matrix with A,B,0 each NxN and 0 an all-zeros matrix. > > What is the necessary and sufficient condition for that matrix to be > orthogonal, i.e. that its transpose also be its inverse? >
by direct computation, AB=BA=0 and A^2+B^2=Id, right?