Multiplicative controllability of the reaction-diffusion equation on a parallelepiped with finitely many zero hyperplanes

We study the global approximate controllability of the reaction-diffusion equation in a parallelpiped $\Omega = (a_1,b_1 ) \times \ldots (a_n,b_n) \subset R^n$, governed by a multiplicative control in a reaction term. It is assumed that the initial state $u_0$ admits zeros only on the intersections of $\Omega$ with finitely many hyperplanes, parallel to the sides of $\Omega$, and that $u_0$ changes its sign after crossing such hyperplanes (we further refer to them as the "hyperplanes of change of sign" or "zero hyperplanes"). This paper can be viewed as a continuation of work presented in \cite{CanKh, CanKh2} for the controllability of the one dimensional reaction-diffusion equation with solutions admitting finitely many zeros. However, the methods of \cite{CanKh, CanKh2} are intrinsically one dimensional, while in this paper we introduce a novel approach to deal with the case of multiple spatial variables.