  We designed and implemented our own versatile simulation software in order to
understand the velocity changes and track patterns observed in slow moving
vortex lattices. The data was obtained from time series of STM images on
NbSe$_2$ in a magnetic field range of 250-750 mT. The main thrust is to explore
possible driving mechanism and to test the effect of various defect
configuration on vortex velocity and tracks. The simulation uses the full
vortex--vortex and vortex--defect interaction. It allows for periodic boundary
conditions as well as a repulsive sample edge. In early versions the time
intervals for recalculating the force were estimated for individual vortices.
This, however, led to a positional 'noise' of unacceptable temperature of the
vortex lattice and was hence replaced by a global time step control. We were
able to produce similar track and velocity patterns as well as local lattice
distortions near point defects as observed by STM. A detailed analysis is,
however, beyond the scope of this paper.
