arXiv subjects
Publications and source records attributed to Yongdo Lim.
We establish the asymptotic regularity and the $Δ$-convergence of the sequence constructed by the alternating projections to closed convex sets in a CAT($κ$) space with $κ> 0$. Furthermore, the strong convergence of the alternating von Neumann sequence is presented under certain regularity or compactness.
We settle an open problem of several years standing by showing that the least-squares mean for positive definite matrices is monotone for the usual (Loewner) order. Indeed we show this is a special case of its appropriate generalization to partially ordered complete metric spaces of nonpositive curvature. Our techniques extend to establish other basic properties of the least squares mean such as continuity and joint concavity. Moreover, we introduce a weighted least squares means and extend our results to this setting.
In this paper we study the problem of extending means to means of higher order. We show how higher order means can be inductively defined and established in general metric spaces, in particular, in convex metric spaces. As a particular application, we consider the positive operators on a Hilbert space under the Thompson metric and show that the operator logarithmic mean admits extensions of all higher orders, thus providing a positive solution to a problem of Petz and Temesi.
Self-scaled barrier functions are fundamental objects in the theory of interior-point methods for linear optimization over symmetric cones, of which linear and semidefinite programming are special cases. We are classifying all self-scaled barriers over irreducible symmetric cones and show that these functions are merely homothetic transformations of the universal barrier function. Together with a decomposition theorem for self-scaled barriers this concludes the algebraic classification theory of these functions. After introducing the reader to the concepts relevant to the problem and tracing the history of the subject, we start by deriving our result from first principles in the important special case of semidefinite programming. We then generalise these arguments to irreducible symmetric cones by invoking results from the theory of Euclidean Jordan algebras.