In variational inference, the VRB is a lower bound on the marginal log likelihood for α < 1, and it is related to the negative of an upper bound on the marginal log likelihood for α > 1, which motivates maximization (cf. minimization) of the VRB for α < 1 (cf. α > 1). The VRB recovers the negative of the reverse KL divergence in the limit α → 0 and extrema of the log likelihood ratios in the left and right limits,