Verriest coauthored this presentation entitled “Reachability of a Cascade of Linear Systems with Communication Delays" with the late Uwe Helmke of the Institute of Mathematics at the Julius Maximilian University of Würzburg in Würzburg, Germany and Paul Fuhrmann of the Department of Mathematics at Ben Gurion University of the Negev in Beer Sheva, Israel. The research is in the area of mathematical systems theory and was conducted while Verriest was on professional development leave in Würzburg last fall.

Verriest and his colleagues derived necessary and sufficient conditions for a notion of "restricted reachability,” when only the states of certain subsystems in a cascade of systems need to be controllable. This is a more general formulation of a motivating problem when a string of robots communicate from one to the next, while the first in the chain receives the control signals. In this case, the states of the communication systems between the robots are of no concern, but the robots' states are. Similarly, the states of a river need to be controlled at certain geographic locations such as population centers, while not as much control is needed in the levels of intermediate floodplains. These conditions, cast in a polynomial systems theoretic framework, generalize the Necessary and Sufficient Condition for full reachability of a cascade, derived by Helmke and Fuhrmann in 2015.