Hydrodynamic instabilities play an important role in the target
compression for inertial confinement fusion (ICF). We present the
analytical solution of a perturbed isentropic implosion. We compare the
analytical solution to the results obtained with perturbation and
bi-dimensional Lagrangian hydrodynamic codes. We also compare results from
bi-dimensional code and perturbation code on an ICF like test case.