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In this manuscript, the concept of dual and approximate dual for continuous frames in Hilbert spaces will be introduced. Some of its properties will be studied. Also, the relations between two continuous Riesz bases in Hilbert spaces will…

Functional Analysis · Mathematics 2017-06-14 Asghar Rahimi , Zahra Darvishi , Bayaz Daraby

We first review the definition of the angle between subspaces and how it is computed using matrix algebra. Then we introduce the Grassmann and Clifford algebra description of subspaces. The geometric product of two subspaces yields the full…

Metric Geometry · Mathematics 2013-06-11 Eckhard Hitzer

The intention of this survey to collect in one paper many recent results and advances related with Bergman type projection acting in various spaces of analytic functions in several complex variables in the unit ball, tubular domains over…

Complex Variables · Mathematics 2025-11-14 R. F. Shamoyan , M. G. Bashmakova

We show that the set of all possible constant diagonals of a bounded Hilbert space operator is always convex. This, in particular, answers an open question of J.-C. Bourin ($2003$). Moreover, we show that the joint numerical range of a…

Functional Analysis · Mathematics 2021-02-16 Vladimir Müller , Yuri Tomilov

We fully characterize orthogonal projections of infinite right circular (round) cones in real Hilbert spaces. Another interpretation is that, given two vectors in a real Hilbert space, we establish the optimal estimate on the angle between…

Functional Analysis · Mathematics 2015-06-30 Mate Kosor

We prove the following result on the timelike spherical Hilbert geometry of simplices: Let $\Delta_2$ be a simplex on the 2-sphere and $\tilde{\Delta}_2$ the antipodal simplex. We show that the timelike spherical Hilbert geometry associated…

Differential Geometry · Mathematics 2023-03-09 Athanase Papadopoulos , Sumio Yamada

We review some basic concepts related to convex real projective structures from the differential geometry point of view. We start by recalling a Riemannian metric which originates in the study of affine spheres using the Blaschke connection…

Geometric Topology · Mathematics 2014-06-30 Inkang Kim , Athanase Papadopoulos

We establish some relations between the perimeter, the area and the visual angle of a planar compact convex set. Our first result states that Crofton's formula is the unique universal formula relating the visual angle, length and area.…

Differential Geometry · Mathematics 2024-04-15 Joaquim Bruna , Julià Cufí , Agustí Reventós

On any proper convex domain in real projective space there exists a natural Riemannian metric, the Blaschke metric. On the other hand, distances between points can be measured in the Hilbert metric. Using techniques of optimal control, we…

Differential Geometry · Mathematics 2021-02-23 Roland Hildebrand

According to the von Neumann-Halperin and Lapidus theorems, in a Hilbert space the iterates of products or, respectively, of convex combinations of orthoprojections are strongly convergent. We extend these results to the iterates of convex…

Functional Analysis · Mathematics 2018-06-05 Catalin Badea , Yuri I. Lyubich

We show that the perimeter of the convex hull of finitely many disks lying in the hyperbolic or Euclidean plane, or in a hemisphere does not increase when the disks are rearranged so that the distances between their centers do not increase.…

Metric Geometry · Mathematics 2017-11-10 Balázs Csikós , Márton Horváth

This paper addresses the numerical computation of critical angles between two convex cones in finite-dimensional Euclidean spaces. We present a novel approach to computing these critical angles by reducing the problem to finding stationary…

Optimization and Control · Mathematics 2023-10-03 Welington de Oliveira , Valentina Sessa , David Sossa

Nearly 15 years ago, a set of qualitative spatial relations between oriented straight line segments (dipoles) was suggested by Schlieder. This work received substantial interest amongst the qualitative spatial reasoning community. However,…

Artificial Intelligence · Computer Science 2009-12-31 Reinhard Moratz , Dominik Lücke , Till Mossakowski

We provide new conditions under which the alternating projection sequence converges in norm for the convex feasibility problem where a linear subspace with finite codimension $N\geq 2$ and a lattice cone in a Hilbert space are considered.…

Optimization and Control · Mathematics 2024-12-16 Francesco Battistoni , Enrico Miglierina

This paper will extend a known relationship between the circumradius and dihedral angles of a tetrahedron in three-dimensional Euclidean space to three-dimensional affine space over a general field not of characteristic two, using only the…

Metric Geometry · Mathematics 2021-01-28 Gennady Arshad Notowidigdo

We prove a sharp lower bound for the fundamental gap on convex domains in Gaussian spaces, the difference between the first two eigenvalues of the Ornstein-Uhlenbeck operator with Dirichlet boundary conditions. Our main result establishes…

Spectral Theory · Mathematics 2025-10-28 Jin Sun , Kui Wang

If we fix the angles at the vertices of a convex planar $n$-gon, the lengths of its edges must satisfy two linear constraints in order for it to close up. If we also require unit perimeter, our vectors of $n$ edge lengths form a convex…

Metric Geometry · Mathematics 2020-02-20 Lyle Ramshaw , James B. Saxe

Reay's relaxed Tverberg conjecture and Conway's thrackle conjecture are open problems about the geometry of pairwise intersections. Reay asked for the minimum number of points in Euclidean d-space that guarantees any such point set admits a…

In a projective space we fix some set of points, a horizon, and investigate the complement of that horizon. We prove, under some assumptions on the size of lines, that the ambient projective space, together with its horizon, both can be…

Combinatorics · Mathematics 2013-05-22 Mariusz Żynel , Krzysztof Petelczyc

We study how the supporting hyperplanes produced by the projection process can complement the method of alternating projections and its variants for the convex set intersection problem. For the problem of finding the closest point in the…

Optimization and Control · Mathematics 2014-02-11 C. H. Jeffrey Pang