  We formulate a gradual dynamical transition from a power-law inflation era
with a scalar field to a radiation era with no scalar field including
inhomogeneous perturbations to the Friedmann- Robertson-Walker universe. We
show that for the cosmic microwave background radiation fluctuations this is
excellently approximated by a sudden transition, with application of the
Lichnerowicz conditions, both for density and gravitational wave perturbations.
