  Mean-field approach has recently been used to model coupled atom-molecular
Bose-Einstein condensates (BEC) and coupled Fermi-Bose condensates near
Feshbach resonance. Sweeping of magnetic field across the resonance gives a new
(nonlinear) version of Landau-Zener problem. We investigate the structure of
the corresponding classical phase space and calculate change in the action
which corresponds to finite-rate efficiency of the sweep. We consider the case
of non-zero initial action, which corresponds to some finite initial molecular
fraction.
