Convex hull property for elliptic and parabolic systems of PDE

Abstract: We study the convex hull property for systems of partial differential equations. This is a generalisation of the maximum principle for a single equation. We show that the convex hull property holds for a class of elliptic and parabolic systems of non-linear partial differential equations. In particular, this includes the case of the parabolic $p$-Laplace system. The coupling conditions for coefficients are demonstrated to be optimal by means of respective counterexamples.