Configuration Flatness of Lagrangian Systems Underactuated by One Control

Lagrangian control systems that are differentially flat with flat outputs that only depend on configuration variables are said to be configuration flat. We provide a complete characterisation of configuration flatness for systems with n degrees of freedom and n - 1 controls whose range of control forces only depends on configuration and whose Lagrangian has the form of kinetic energy minus potential. The method presented allows us to determine if such a system is configuration flat and, if so provides a constructive method for finding all possible configuration flat outputs. Our characterisation relates configuration flatness to Riemannian geometry. We illustrate the method by two examples

A Test for Differential Flatness by Reduction to Single Input Systems

For nonlinear control systems (p inputs), we present a test for flatness. The method consists of making an initial guess for p-1 of the flat outputs, which may involve parameters still to be determined. A choice of functions of time for the p-1 outputs reduce the system to one with a single input. For single input systems the problem of flatness has been solved and thus leads to the identification of the last flat output, or to obstructions to flatness under the hypotheses. We demonstrate the method for a coupled rigid body in ℝ2 and for a single rigid body in ℝ3

Large population and long-term behavior of a stochastic binary opinion model

We propose and study a stochastic binary opinion model where agents in a group are considered to hold an opinion of 0 or 1 at each moment. An agent in the group updates his/her opinion based on the group's opinion configuration and his/her \emph{personality}. Considering the number of agents with opinion 1 as a continuous time Markov process, we analyze the long-term probabilities for large population size in relation to the personalities of the group. In particular, we focus on the question of "balance" where both opinions are present in nearly equal numbers as opposed to "dominance" where one opinion is dominant