  We optimize the classical field approximation of the version described in J.
Phys. B 40, R1 (2007) for the oscillations of a Bose gas trapped in a harmonic
potential at nonzero temperatures, as experimentally investigated by Jin et al.
[Phys. Rev. Lett. 78, 764 (1997)]. Similarly to experiment, the system response
to external perturbations strongly depends on the initial temperature and on
the symmetry of perturbation. While for lower temperatures the thermal cloud
follows the condensed part, for higher temperatures the thermal atoms oscillate
rather with their natural frequency, whereas the condensate exhibits a
frequency shift toward the thermal cloud frequency (m=0 mode), or in the
opposite direction (m=2 mode). In the latter case, for temperatures approaching
critical, we find that the condensate begins to oscillate with the frequency of
the thermal atoms, as in the m=0 mode. A broad range of frequencies of the
perturbing potential is considered.
