  The analytical continuation average spectrum method (ASM) and maximum entropy
(MaxEnt) method are applied to the dynamic response of a noninteracting
resonant level model within the framework of the Kubo formula for electric
conductivity. The frequency dependent conductivity is inferred from the
imaginary time current-current correlation function for a wide range of
temperatures, gate voltages and spectral densities representing the leads, and
compared with exact results. We find that the MaxEnt provides more accurate
results compared to the ASM over the full spectral range.
