Amenable cones: error bounds without constraint qualifications

We provide a framework for obtaining error bounds for linear conic problems without assuming constraint qualifications or regularity conditions. The key aspects of our approach are the notions of amenable cones and facial residual functions. For amenable cones, it is shown that error bounds can be expressed as a composition of facial residual functions. The number of compositions is related to the facial reduction technique and the singularity degree of the problem. In particular, we show that symmetric cones are amenable and compute facial residual functions. From that, we are able to furnish a new H\"olderian error bound, thus extending and shedding new light on an earlier result by Sturm on semidefinite matrices. We also provide error bounds for the intersection of amenable cones, this will be used to provided error bounds for the doubly nonnegative cone.Comment: 36 pages, 1 figure. This version was significantly revised. A discussion on the relation between amenability and related concepts was added. In particular, there is a proof that amenable cones are nice and, therefore, facially exposed. Also, gathered the results on symmetric cones in a single section. Several typos and minor issues were fixe

The automorphism group and the non-self-duality of pp-cones

In this paper, we determine the automorphism group of the $p$-cones ($p\neq 2$) in dimension greater than two. In particular, we show that the automorphism group of those $p$-cones are the positive scalar multiples of the generalized permutation matrices that fix the main axis of the cone. Next, we take a look at a problem related to the duality theory of the $p$-cones. Under the Euclidean inner product it is well-known that a $p$-cone is self-dual only when $p=2$. However, it was not known whether it is possible to construct an inner product depending on $p$ which makes the $p$-cone self-dual. Our results shows that no matter which inner product is considered, a $p$-cone will never become self-dual unless $p=2$ or the dimension is less than three.Comment: 17 pages, 2 figures. Comments welcom

Generalized subdifferentials of spectral functions over Euclidean Jordan algebras

This paper is devoted to the study of generalized subdifferentials of spectral functions over Euclidean Jordan algebras. Spectral functions appear often in optimization problems playing the role of "regularizer", "barrier", "penalty function" and many others. We provide formulae for the regular, approximate and horizon subdifferentials of spectral functions. In addition, under local lower semicontinuity, we also furnish a formula for the Clarke subdifferential, thus extending an earlier result by Baes. As application, we compute the generalized subdifferentials of the function that maps an element to its k-th largest eigenvalue. Furthermore, in connection with recent approaches for nonsmooth optimization, we present a study of the Kurdyka-Lojasiewicz (KL) property for spectral functions and prove a transfer principle for the KL-exponent. In our proofs, we make extensive use of recent tools such as the commutation principle of Ram\'irez, Seeger and Sossa and majorization principles developed by Gowda.Comment: 26 pages. Some minor fixes and trimming. Accepted for publication at the SIAM Journal on Optimizatio

Characterization and space embedding of directed graphs and social networks through magnetic Laplacians

Though commonly found in the real world, directed networks have received relatively less attention from the literature in which concerns their topological and dynamical characteristics. In this work, we develop a magnetic Laplacian-based framework that can be used for studying directed complex networks. More specifically, we introduce a specific heat measurement that can help to characterize the network topology. It is shown that, by using this approach, it is possible to identify the types of several networks, as well as to infer parameters underlying specific network configurations. Then, we consider the dynamics associated with the magnetic Laplacian as a means of embedding networks into a metric space, allowing the identification of mesoscopic structures in artificial networks or unravel the polarization on political blogosphere. By defining a coarse-graining procedure in this metric space, we show how to connect the specific heat measurement and the positions of nodes in this space

Exact augmented Lagrangian functions for nonlinear semidefinite programming

In this paper, we study augmented Lagrangian functions for nonlinear semidefinite programming (NSDP) problems with exactness properties. The term exact is used in the sense that the penalty parameter can be taken appropriately, so a single minimization of the augmented Lagrangian recovers a solution of the original problem. This leads to reformulations of NSDP problems into unconstrained nonlinear programming ones. Here, we first establish a unified framework for constructing these exact functions, generalizing Di Pillo and Lucidi's work from 1996, that was aimed at solving nonlinear programming problems. Then, through our framework, we propose a practical augmented Lagrangian function for NSDP, proving that it is continuously differentiable and exact under the so-called nondegeneracy condition. We also present some preliminary numerical experiments.Comment: 26 pages. Added journal referenc

Facial Reduction and Partial Polyhedrality

We present FRA-Poly, a facial reduction algorithm (FRA) for conic linear programs that is sensitive to the presence of polyhedral faces in the cone. The main goals of FRA and FRA-Poly are the same, i.e., finding the minimal face containing the feasible region and detecting infeasibility, but FRA-Poly treats polyhedral constraints separately. This idea enables us to reduce the number of iterations drastically when there are many linear inequality constraints. The worst case number of iterations for FRA-poly is written in the terms of a "distance to polyhedrality" quantity and provides better bounds than FRA under mild conditions. In particular, in the case of the doubly nonnegative cone, FRA-Poly gives a worst case bound of $n$ whereas the classical FRA is $\mathcal{O}(n^2)$. Of possible independent interest, we prove a variant of Gordan-Stiemke's Theorem and a proper separation theorem that takes into account partial polyhedrality. We provide a discussion on the optimal facial reduction strategy and an instance that forces FRAs to perform many steps. We also present a few applications. In particular, we will use FRA-poly to improve the bounds recently obtained by Liu and Pataki on the dimension of certain affine subspaces which appear in weakly infeasible problems.Comment: A few typo corrections. The proof of Lemma 3 was rewritten. To appear in the SIAM Journal on Optimization. Comments are welcom

Bimodal pattern in the fragmentation of Au quasi-projectiles

Signals of bimodality have been investigated in experimental data of quasi-projectile decay produced in Au+Au collisions at 35 AMeV. This same data set was already shown to present several signals characteristic of a first order, liquid-gas-like phase transition. For the present analysis, events are sorted in bins of transverse energy of light charged particles emitted by the quasi-target source. A sudden change in the fragmentation pattern is observed from the distributions of the asymmetry of the two largest fragments, and the charge of the largest fragment. This latter distribution shows a bimodal behavior. The interpretation of this signal is discussed.Comment: 8 pages, 11 figures, submitted to European Physical Journal

A structural geometrical analysis of weakly infeasible SDPs

In this article, we present a geometric theoretical analysis of semidefinite feasibility problems (SDFPs). This is done by decomposing a SDFP into smaller problems, in a way that preserves most feasibility properties of the original problem. With this technique, we develop a detailed analysis of weakly infeasible SDFPs to understand clearly and systematically how weak infeasibility arises in semidefinite programming. In particular, we show that for a weakly infeasible problem over $n\times n$ matrices, at most $n-1$ directions are required to approach the positive semidefinite cone. We also present a discussion on feasibility certificates for SDFPs and related complexity results.Comment: This version contains a shorter and more focused discussion. Proposition 19 and Theorem 23 in the previous version now correspond to Proposition 6 and Theorem 10. We also tried to contextualize some of the results in the BSS model. The first version will stay available at http://www.optimization-online.org/DB_HTML/2013/11/4137.html as well. 14 page

Perfect and flexible quantum state transfer in the hybrid system atom coupled-cavity

We investigate a system composed of $N$ coupled cavities and two-level atoms interacting one at a time. Adjusting appropriately the atom-field detuning, and make the hopping rate of photons between neighboring cavities, $A$, greater than the atom-field coupling $g$ (i.e. $A>>g$), we can eliminate the interaction of the atom with the nonresonant normal modes reducing the dynamics to the interaction of the atom with only a single-mode. As an application of this interaction, we analyze the transmission of an arbitrary atomic quantum state between distant coupled cavities. In the ideal case, we obtain a flexible and perfect quantum communication. Considering the influence of dissipation an interesting parity effect emerge and we obtain $N$ maximum in which it is still possible to achieve a quantum communication more efficient than a purely classical channel between the ends. We also studied important sources of imperfections in procedure execution.Comment: 14 pages, 7 figures, IOP styl