  Stability of synchronization in unidirectionally coupled time-delay systems
is studied using the Krasovskii-Lyapunov theory. We have shown that the same
general stability condition is valid for different cases, even for the general
situation (but with a constraint) where all the coefficients of the error
equation corresponding to the synchronization manifold are time-dependent.
These analytical results are also confirmed by numerical simulation of
paradigmatic examples.
