  Numerical simulations of vortex motion in a trapped Bose-Einstein condensate
were performed by solving the two-dimensional Gross-Pitaevskii equation in the
presence of a simple phenomenological model of interaction between the
condensate and the finite temperature thermal cloud. The log (base e) of total
energy, trap energy, quantum energy, kinetic energy, internal energy and
z-component of the angular momentum vs time were compared with f(x)=a+bx for
that time when the vortices come in in the condensate. The increasing/decay
rate of these energies and L_{z} were studied as a function of dissipation.
