  The dynamic critical exponent z is determined from numerical simulations for
the three-dimensional XY model subject to two types of dynamics, i.e.
relaxational dynamics and resistively shunted junction (RSJ) dynamics, as well
as for two different treatments of the boundary, i.e., periodic boundary
condition (PBC) and fluctuating twist boundary condition (FTBC). In case of
relaxational dynamics, finite size scaling at the critical temperature gives
$z\approx 2$ for PBC and 1.5 for FTBC, while for RSJ dynamics $z\approx 1.5$ is
obtained in both cases. The results are discussed in the context of
superfluid/superconductors and vortex dynamics, and are compared with what have
been found for other related models.
