Observers and Relative Entropy Functional
In this paper, we will use the mathematical modeling of one-dimensional observers to present the notion of the \emph{relative entropy functional} for relative dynamical systems. Also, the invariance of the entropy of a system under topological conjugacy is generalized to the relative entropy functional. Moreover, from observer viewpoint, a new version of the Jacobs Theorem is obtained. It has been proved that relative entropy functional is equivalent to the Kolmogorov entropy for dynamical systems, from the viewpoint of observer $ \chi_X $, where $ \chi_X $ is the characteristic function on compact metric space $X$.