In this paper we give a complete answer to the famous gradient problem of C. E. Weil. On an open set G ⊂ R2 we construct a differentiable function f: G → R for which there exists an open set Ω1 ⊂ R2 such that ∇f(p) ∈ Ω1 for a p ∈ G but ∇f(q) ∉ Ω1 for almost every q ∈ G. This shows that the Denjoy-Clarkson property does not hold in higher dimensions.
In this paper we revisit Haff's seminal work on the matrix Haffian as we proposed to call it. We review some results, and give new derivations. Use is made of the link between the matrix Haffian ∇F and the differential of the matrix function, dF.
We establish some criteria for a nonsingular square matrix depending on several parameters to be represented in the form of a matrix product of factors which depend on the single parameters.
Using generalized absolute continuity, we characterize additive interval functions which are indefinite Henstock-Kurzweil integrals in the Euclidean space.
We present a stability theorem of Ulam-Hyers type for K-convex set-valued functions, and prove that a set-valued function is K-convex if and only if it is K-midconvex and K-quasiconvex.
Some limit and Dieudonné-type theorems in the setting of (ℓ)-groups with respect to filter convergence are proved, extending earlier results.
∗ Cette recherche a été partiellement subventionnée, en ce qui concerne le premier et le dernier auteur, par la bourse OTAN CRG 960360 et pour le second auteur par l’Action Intégrée 95/0849 entre les universités de Marrakech, Rabat et Montpellier.The primary goal of this paper is to shed some light on the maximality of the pointwise sum of two maximal monotone operators. The interesting purpose is to extend some recent results of Attouch, Moudafi and Riahi on the graph-convergence of maximal monotone...
On montre que toute fonction positive de classe définie sur un intervalle de est somme de deux carrés de fonctions de classe . En dimension 2, toute fonction positive de classe est somme d’un nombre fini de carrés de fonctions de classe , pourvu que ses dérivées d’ordre 4 s’annulent aux points où et s’annulent.
It is shown that every closed rotation and translation invariant subspace of or , , is of spectral synthesis, i.e. is spanned by the polynomial-exponential functions it contains. It is a classical problem to find those measures of compact support on with the following property: (P) The only function satisfying for all rigid motions of is the zero function. As an application of the above result a characterization of such measures is obtained in terms of their Fourier-Laplace transforms....