text: When the Landau constant is negative, , we must include a negative term of higher order to arrest the unbounded increase of the perturbation. In this case, the Landau equation becomes
  The limiting amplitude then becomes
  where the plus sign corresponds to the stable branch and the minus sign to the unstable branch. There exists a value of a critical value  where the above two roots are equal () such that , indicating that the flow in the region  is metastable', that is to say, in the metastable region, the flow is stable to infinitesimal perturbations, but not to finite amplitude perturbations.