Outward pointing properties for vectorial hysteresis operators and some applications Abstract. In a number of papers, the concept of outward pointing hysteresis allowed the application of the method of invariant regions to derive uniform bounds for solutions to evolution equations involving scalar hysteresis operators and input perturbations.The aim of this note is to generalize the "pointing outward" properties to vectorial hysteresis operators, and to show how these properties can be used to derive uniform estimates for differential equations involving vectorial hysteresis operators and input perturbations.
Introduction and statement of the problemThe method of invariant regions is quite often used to derive uniform estimates for solutions to evolution equations involving nonlinear scalar superposition operators and some input perturbations, such that asymptotic stability results can be shown, see, e.g., [16,17].In a number of papers, the concept of outward pointing hysteresis allowed the application of the method of invariant regions also to evolution equations involving scalar hysteresis operators and input perturbations, see [2,3,7,8,9,10,11].The aim of this note is to generalize the "pointing outward" properties to vectorial hysteresis operators, and to show how these properties can be used to derive uniform estimates for differential equations involving vectorial hysteresis operators and input perturbations.After recalling the definition of hysteresis operators in Section 2, in Section 3 the outward pointing definitions for scalar hysteresis operators will be recalled and some theorems will show that one can derive uniform bounds for evolution equations with hysteresis operators in a similar way as is done with the method of invariant regions for evolution equations with superposition operators.In Section 4, the definition of the outward pointing condition for vectorial hysteresis operators will be formulated, some examples for vectorial operators satisfying this condition will be presented, and it will be shown how one can derive uniform bounds for ODEs involving this kind of operator. Moreover, there will be a discussion of which problems arise if one also takes input perturbations into account. To overcome these problems, the more restrictive componentwise outward pointing condition for vectorial hysteresis operators is introduced in Section 5, and uniform estimates for ODEs with componentwise outward pointing vectorial hysteresis operators and input perturbations are derived.