We show that the energy–momentum equations arising from inner variations whose Lagrangian satisfies a generic symmetry condition are ill-posed. This is done by proving that there exists a subclass of Lipschitz solutions that are also solutions to a differential inclusion into the orthogonal group and in particular these solutions can be nowhere $C^1$. We prove that these solutions are not stationary points if the Lagrangian $W$ is $C^1$ and strictly rank-one convex. In view of the Lipschitz regularity result of Iwaniec, Kovalev and Onninen for solution of the energy–momentum equation in dimension 2, we give a sufficient condition for the non-existence of a partial $C^1$ -regularity result even under the condition that the mappings satisfy a positive Jacobian determinant condition. Finally, we consider a number of well-known functionals studied in non-linear elasticity and geometric function theory and show that these do not satisfy this obstruction to partial regularity.

In this work we are concerned with the existence of fixed points for multivalued maps defined on Banach spaces. Using the Banach spaces scale concept, we establish the existence of a fixed point of a multivalued map in a vector subspace where the map is only locally Lipschitz continuous. We apply our results to the existence of mild solutions and asymptotically almost periodic solutions of an abstract Cauchy problem governed by a first-order differential inclusion. Our results are obtained by using fixed point theory for the measure of noncompactness.

Non-smooth approximations of steep sigmoidal switching networks, such as those used as qualitative models of gene regulation, lead to analytic and computational challenges that arise as a result of the discontinuities in the vector fields. In order to highlight the need for care in dealing with such systems, several particular phenomena are presented here through illustrative examples, including ‘Zeno breaking’, or computing beyond the finite time convergence of an infinite sequence of threshold transitions; the ‘Contact’ effect, in which in the discontinuous limit, trajectories can pass through a ‘saddle point’ without stopping, though these solutions are not unique and other solutions stop for arbitrary time intervals; and sensitive behaviour that arises from exotic dynamics within switching regions.

We study an abstract second order inclusion involving two nonlinear single-valued operators and a nonlinear multi-valued term. Our goal is to establish the existence of solutions to the problem by applying numerical scheme based on time discretization. We show that the sequence of approximate solution converges weakly to a solution of the exact problem. We apply our abstract result to a dynamic, second-order-in-time differential inclusion involving a Clarke subdifferential of a locally Lipschitz, possibly non-convex and non-smooth potential. In the two presented examples the Clarke subdifferential appears either in a source term or in a boundary term.

Using a variational approach we obtain the existence of at least three periodic solutions for discontinuous perturbations of the vector p-Laplacian operator .

In the nonconvex case, solutions of rate-independent systems may develop jumps as afunction of time. To model such jumps, we adopt the philosophy that rate-independenceshould be considered as limit of systems with smaller and smaller viscosity. For thefinite-dimensional case we study the vanishing-viscosity limit of doubly nonlinearequations given in terms of a differentiable energy functional and a dissipation potentialthat is a viscous regularization of a given rate-independent dissipation potential. Theresulting definition of “BV solutions” involves, in a nontrivial way, both therate-independent and the viscous dissipation potential, which play crucial roles in thedescription of the associated jump trajectories. We shall prove general convergenceresults for the time-continuous and for the time-discretized viscous approximations andestablish various properties of the limiting BV solutions. In particular, we shall providea careful description of the jumps and compare the new notion of solutions with therelated concepts of energetic and local solutions to rate-independent systems.

Several recent results in the area of robust asymptotic stability of hybrid systems show that the concept of a generalized solution to a hybrid system is suitable for the analysis and design of hybrid control systems. In this paper, we show that such generalized solutions are exactly the solutions that arise when measurement noise in the system is taken into account.

For a large class of operator inclusions, including those generated by maps of pseudomonotone type, we obtain a general theorem on existence of solutions. We apply this result to some particular examples. This theorem is proved using the method of difference approximations.

We propose a necessary and sufficient condition about the existence of variations, i.e.,of non trivial solutions $\eta\in W^{1,\infty}_0(\Omega)$ to the differential inclusion $\nabla\eta(x)\in-\nabla u(x)+{\bf D}$ .

In this article, we show the convergence of a class of numerical schemes for certain maximal monotone evolution systems; a by-product of this resultsis the existence of solutions in cases which had not been previouslytreated. The order of these schemes is 1/2 in general and 1 when the only non Lipschitz continuous term is the subdifferential of the indicatrix of a closed convex set. In the case of Prandtl'srheological model, our estimates in maximum norm do not dependon spatial dimension.

We consider differential inclusions wherea positive semidefinite function of the solutions satisfies aclass- ${\mathcal{KL}}$ estimatein terms of time and a second positive semidefinite function of theinitial condition.We show that a smooth converse Lyapunov function, i.e., one whosederivative along solutions can beused to establish the class- ${\mathcal{KL}}$ estimate, exists if andonly if the class- ${\mathcal{KL}}$ estimateis robust, i.e., it holds for a larger, perturbed differentialinclusion.It remains an open question whether all class- ${\mathcal{KL}}$ estimates are robust.One sufficient condition for robustness is that the originaldifferential inclusion is locally Lipschitz.Another sufficient condition is that the two positive semidefinitefunctions agree anda backward completability condition holds. These special cases unifyand generalize many resultson converse Lyapunov theorems for differential equations anddifferential inclusions that have appeared in the literature.