Controllability Problems for the Heat Equation in a Half-Plane Controlled by the Neumann Boundary Condition with a Point-Wise Control

TL;DR

This paper investigates controllability of the heat equation in a half-plane with boundary control via a point-wise Neumann boundary condition, providing necessary and sufficient conditions, and reducing the problem to a Markov moment problem.

Contribution

It introduces a novel reduction of the controllability problem to a Markov moment problem and characterizes the reachable states for the heat equation with point-wise boundary control.

Findings

Characterization of reachable states as functions of a specific form

Necessary and sufficient conditions for controllability and approximate controllability

Demonstration of the non-null-controllability of initial states within finite time

Abstract

In the paper, the problems of controllability and approximate controllability are studied for the control system $w_t=\Delta w$, $w_{x_1}(0,x_2,t)=u(t)\delta(x_2)$, $x_1>0$, $x_2\in\mathbb R$, $t\in(0,T)$, where $u\in L^\infty(0,T)$ is a control. To this aid, it is investigated the set $\mathcal{R}_T(0)\subset L^2((0,+\infty)\times\mathbb R)$ of its end states which are reachable from $0$. It is established that a function $f\in\mathcal{R}_T(0)$ can be represented in the form $f(x)=g\big(|x|^2\big)$ a.e. in $(0,+\infty)\times\mathbb R$ where $g\in L^2(0,+\infty)$. In fact, we reduce the problem dealing with functions from $L^2((0,+\infty)\times\mathbb R)$ to a problem dealing with functions from $L^2(0,+\infty)$. Both a necessary and sufficient condition for controllability and a sufficient condition for approximate controllability in a given time $T$ under a control $u$ bounded by a given constant are obtained in terms of solvability of a Markov power moment problem. Using the Laguerre functions (forming an orthonormal basis of $L^2(0,+\infty)$), necessary and sufficient conditions for approximate controllability and numerical solutions to the approximate controllability problem are obtained. It is also shown that there is no initial state that is null-controllable in a given time $T$. The results are illustrated by an example.