PROOF. As mentioned earlier a sufficient, though not necessary condition
that the matrices R and R be similar is, of course, that A and B have
no common characteristic root. In this case a solution of (1.1) not only
exists, but is unique. But this is also necessary for the hypothesis here
implies that f(B)=0, whence f,(A) is a multiple of the minimum polynomial
of B, and that V=fa(A) is nonsingular, whence f,(A) cannot
vanish for any characteristic root of A.