In this paper we introduce a new functional invariant of discrete time
dynamical systems -- the so-called t-entropy. The main result is that this
t-entropy is the Legendre dual functional to the logarithm of the spectral
radius of the weighted shift operator on L1(X,m) generated by the dynamical
system. This result is called the Variational principle and is similar to the
classical variational principle for the topological pressure.Comment: 12 pages, v.2: editorial correction