  Photoabsorption spectrum of the Xe@C$_{60}$ endohedral fullerene has been
studied using the time-dependent-density-functional-theory (TDDFT), which
represents the dynamical polarizability of an interacting electron system by an
off-diagonal matrix element of the resolvent of the Liouvilliam superoperator
and solves the problem with the Lanczos algorithm. The method has been tested
with the photoabsorption cross sections of the free Xe atom and C$_{60}$
fullerene. The result for the Xe@C$_{60}$ confirms the three main peaks
observed in the recent measurement in the energy region of the Xe 4$d$ giant
resonance and demonstrates the underestimation of the photoionization cross
section by the experiment. It is suggested to use the current theoretical
result around 22 eV to calibrate the experimental data.
