ИСТИНА

Unbounded keplerian flows are known to be dynamically stable to adiabatic perturbations. The same can be concluded about axisymmetric tori with quasi-keplerian rotation, since the known sonic instability due to the coupling of sound modes ceases rapidly as one suppresses the torus thickness. Despite this boring picture we show that a prominent transient growth of optimal perturbations is possible both in quasi-keplerian tori and in infinite keplerian discs. These optimal perturbations are determined using an iterative scheme for cauchy problem for direct and adjoint hydrodynamical equations.