  A simple approach is proposed allowing actual calculations of the
preequilibrium dynamics in ultrarelativistic heavy-ion collisions to be
performed for a far-from-equilibrium initial state. The method is based on the
phenomenological macroscopic equations that describe the relaxation dynamics of
the energy-momentum tensor and are motivated by Boltzmann kinetics in the
relaxation-time approximation. It gives the possibility to match smoothly a
nonthermal initial state to the hydrodynamics of the quark gluon plasma. The
model contains two parameters, the duration of the prehydrodynamic stage and
the initial value of the relaxation-time parameter, and allows one to assess
the energy-momentum tensor at a supposed time of initialization of the
hydrodynamics.
