  We study the stability and sensitivity of an absorbing layer for the
Boltzmann equation by examining the Bhatnagar-Gross-Krook (BGK) approximation
and using the perfectly matched layer (PML) technique. To ensure stability, we
discard some parameters in the model and calculate the total sensitivity
indices of the remaining parameters using the ANOVA expansion of multivariate
functions. We conduct extensive numerical experiments on two test cases to
study stability and compute the total sensitivity indices, which allow us to
identify the essential parameters of the model.
