“…Although A-stability does not imply B-stability, the closely related concepts of AN and BN-stability are equivalent. The matrix M , which plays a central role in B-stability, has since become of crucial importance in the study of canonical Runge-Kutta methods [4] which respect quadratic invariants. Suppose y, Qy is a quadratic invariant, so that f (y), Qy = 0, then, noting that (6) still holds if the inner product ·, · is replaced by ·, Q· , we see that, if M = 0, y n , Qy n = y n−1 , Qy n−1 , indicating that invariance is preserved by numerical approximations.…”