  In this note we discuss the construction of high order asymptotic preserving
numerical schemes for the Boltzmann equation. The methods are based on the use
of Implicit-Explicit (IMEX) Runge-Kutta methods combined with a penalization
technique recently introduced in [F. Filbet, S. Jin: A class of asymptotic
preserving schemes for kinetic equations and related problems with stiff
sources,J. Comp. Phys. 229, (2010), pp. 7625-7648.].
