On page 6 of Duffie's book (third edition) has this function: g_theta(\alpha) = U (c + \alpha D^T \theta) Then it passes to : (g_theta(0))' = dU(c)^T * D^T * \theta I do not see where he got the transpose sign on dU(c). Maybe it is very obvious. Can anyone elighten me? Thanks, - Carpe Diem