We study the problem of determining in a constructive way a convex body in the plane from its tomographic projections. For this, we consider the similar problem in digital plane: reconstructing a lattice convex set from its discrete tomographic projection. We show that we can use a reconstruction algorithm for the discrete problem to solve the continuous reconstruction to any precision. The pro...

Let R(∂) be a matrix whose entries are linear partial differential operators, with constant coefficients. Let Ω be a non-empty, open, bounded, convex set. We consider the homogeneous system R(∂)f = 0 in a neighborhood of Ω, subject to the boundary condition f = g in a neighborhood of ∂Ω. For a given smooth function g, we give a criterion for the (unique) existence of a smooth solution f to this...

In this paper, we study the rate of convergence of the cyclic projection algorithm applied to finitely many basic semi-algebraic convex sets. We establish an explicit convergence rate estimate which relies on the maximum degree of the polynomials that generate the basic semi-algebraic convex sets and the dimension of the underlying space. We achieve our results by exploiting the algebraic struc...

Abstract An elimination problem in semidefinite programming is solved by means of tensor algebra. It concerns families of matrix cube problems whose constraints are the minimum and maximum eigenvalue function on an affine space of symmetric matrices. An LMI representation is given for the convex set of all feasible instances, and its boundary is studied from the perspective of algebraic geometr...

In this paper, we consider a family of closed planar algebraic curves C which are given in parametrization form via a trigonometric polynomial p. When C is the boundary of a compact convex set, the polynomial p represents the support function of this set. Our aim is to examine properties of the degree of the defining polynomial of this family of curves in terms of the degree of p. Thanks to the...

In this paper we study big convexity theories, that is convexity theories that are not necessarily bounded. As in the bounded case (see [4]) such a convexity theory Γ gives rise to the category ΓC of (left) Γ-convex modules. This is an equationally presentable category, and we prove that it is indeed an algebraic category over Set. We also introduce the category ΓAlg of Γ-convex algebras and sh...

and Applied Analysis 3 Lemma 2.4 see 9, Lemma 3.1 . Let X, Y, and Z be three topological spaces. Let Y be compact, F : X × Y ⇒ Z a set-valued mapping, and the set-valued mapping T : X ⇒ Z defined by T x ⋃ y∈Y F ( x, y ) , ∀x ∈ X. 2.2 a If F is upper semi-continuous on X × Y, then T is upper semi-continuous on X. b If F is lower semi-continuous onX, so is T. Lemma 2.5 see 9, Lemma 3.2 . Let Z be...

where b ranges over a set BExp of boolean expressions, a ranges over a set Act of basic actions and p is a real number with 0 < p < 1. The aim of the current paper is to perform this task for the partial correctness case where the direct semantics of a program P is given by a function from the set S of states to PLV(S), the convex lower powerdomain of valuations on S. Here V(S) is the set of al...

The Happy End Theorem of Erdős and Szekeres asserts that for every integer n greater than two there is an integer N such that every set of N points in general position in the plane includes the n vertices of a convex n-gon. We generalize this theorem in the framework of certain simple structures, which we call “happy end spaces”. In the winter of 1932/33, Esther Klein observed that from any set...

Let V be a real linear space. The functor ConvexComb(V ) yielding a set is defined by: (Def. 1) For every set L holds L ∈ ConvexComb(V ) iff L is a convex combination of V . Let V be a real linear space and let M be a non empty subset of V . The functor ConvexComb(M) yielding a set is defined as follows: (Def. 2) For every set L holds L ∈ ConvexComb(M) iff L is a convex combination of M . We no...