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Baes M.,ETH Zurich | Del Pia A.,ETH Zurich | Nesterov Y.,CORE | Onn S.,Technion - Israel Institute of Technology | Weismantel R.,ETH Zurich
Mathematical Programming | Year: 2012

This paper is about theminimization of Lipschitz-continuous and strongly convex functions over integer points in polytopes. Our results are related to the rate of convergence of a black-box algorithm that iteratively solves special quadratic integer problems with a constant approximation factor. Despite the generality of the underlying problem, we prove that we can find efficiently, with respect to our assumptions regarding the encoding of the problem, a feasible solution whose objective function value is close to the optimal value. We also show that this proximity result is the best possible up to a factor polynomial in the encoding length of the problem. © Springer and Mathematical Optimization Society 2012.

Traag V.A.,avenue G. Lemaitre | Nesterov Y.E.,CORE | Van Dooren P.,avenue G. Lemaitre
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2010

Networks have attracted a great deal of attention the last decade, and play an important role in various scientific disciplines. Ranking nodes in such networks, based on for example PageRank or eigenvector centrality, remains a hot topic. Not only does this have applications in ranking web pages, it also allows peer-to-peer systems to have effective notions of trust and reputation and enables analyses of various (social) networks. Negative links however, confer distrust or dislike as opposed to positive links, and are usually not taken into account. In this paper we propose a ranking method we call exponential ranking, which allows for negative links in the network. We show convergence of the method, and demonstrate that it takes into account negative links effectively. © 2010 Springer-Verlag.

Leidy N.K.,Center for Health Outcomes Research | Wilcox T.K.,Center for Health Outcomes Research | Jones P.W.,University of London | Jones P.,University of London | And 11 more authors.
American Journal of Respiratory and Critical Care Medicine | Year: 2011

Rationale: Although exacerbations are an important problem in chronic obstructive pulmonary disease (COPD) and a target of intervention, there is no valid, standardized tool for assessing their frequency, severity, and duration. Objectives: This study tested the properties of the Exacerbations of Chronic Pulmonary Disease Tool (EXACT), a new patient-reported outcome diary. Methods: A prospective, two-group, observational study was conducted in patients with COPD. The acute group (n = 222) was enrolled during a clinic visit for exacerbation with follow-up visits on Days 10, 29, and 60. The stable group (n = 188), recruited by telephone or during routine visits, was exacerbation free for at least 60 days. Measurements and Main Results: Acute patients completed the diary on Days 1-29 and 60-67; stable patients for 7 days. All patients provided stable-state spirometry and completed the St. George Respiratory Questionnaire-COPD (SGRQ-C). Acute patient assessments included clinician and patient global ratings of exacerbation severity and recovery. Mean age of the sample (n = 410) was 65 (± 10) years; 48% were male; stable FEV1 was 51% predicted (± 20). Internal consistency (Pearson separation index) for the EXACT was 0.92, 1-week reproducibility (stable patients; intraclass correlation) was 0.77. EXACT scores correlated with SGRQ-C (r = 0.64; P < 0.0001) and differentiated acute and stable patients (P<0.0001). In acute patients, scores improved over time (P < 0.0001) and differentiated between degrees of clinician-rated exacerbation severity (P < 0.05). EXACT change scores differentiated responders and nonresponders on Day 10, as judged by clinicians or patients (P < 0.0001). Conclusions: Results suggest the EXACT is reliable, valid, and sensitive to change with exacerbation recovery.

Straney L.D.,Monash University | Schlapbach L.J.,University of Queensland | Schlapbach L.J.,Paediatric Intensive Care Unit | Schlapbach L.J.,Gold Coast University Hospital | And 7 more authors.
Pediatric Critical Care Medicine | Year: 2015

Objectives: To describe the temporal trends in rates of PICU admissions and mortality for out-of-hospital cardiac arrests and in-hospital cardiac arrests admitted to PICU over the last decade. Design: Multicenter, retrospective analysis of prospectively collected binational data of the Australian and New Zealand Paediatric Intensive Care Registry. All nine specialist PICUs in Australia and New Zealand were included. Patients: All children admitted between 2003 and 2012 to PICU who were less than 16 years old at the time of admission. Interventions: None. Measurements and Main Results: There were a total of 71,425 PICU admissions between 2003 and 2012. Overall, cardiac arrest accounted for 1.86% of all admissions (1,329 cases), including 677 cases of in-hospital cardiac arrest (51.0%) and 652 cases of out-of-hospital cardiac arrest (49.0%). Over the last decade, there has been a 29.6% increase in the odds of PICU survival for all pediatric admissions (odds ratio, 1.30; 95% CI, 1.09-1.54). By contrast, there was no significant improvement in the risk-adjusted odds of survival for out-of-hospital cardiac arrest admissions (odds ratio, 1.03; 95% CI, 0.50-2.10; p = 0.94) or in-hospital cardiac arrest admissions (odds ratio, 1.03; 95% CI, 0.54-1.98; p = 0.92). Conclusions: Despite improvements in overall outcomes in children admitted to Australian and New Zealand PICUs, survival of children admitted with out-of-hospital cardiac arrest or in-hospital cardiac arrest did not change significantly over the past decade. © 2015 by the Society of Critical Care Medicine and the World Federation of Pediatric Intensive and Critical Care Societies.

Van Vyve M.,CORE
Mathematical Programming | Year: 2013

In the fixed-charge transportation problem, the goal is to optimally transport goods from depots to clients when there is a fixed cost associated to transportation or, equivalently, to opening an arc in the underlying bipartite graph. We further motivate its study by showing that it is both a special case and a strong relaxation of the big-bucket multi-item lot-sizing problem, and a generalization of a simple variant of the single-node flow set. This paper is essentially a polyhedral analysis of the polynomially solvable special case in which the associated bipartite graph is a path. We give a O (n3)-time optimization algorithm and a O (n2) -size linear programming extended formulation. We describe a new class of inequalities that we call "path-modular" inequalities. We give two distinct proofs of their validity. The first one is direct and crucially relies on sub- and super-modularity of an associated set function. The second proof is by showing that the projection of the extended linear programming formulations onto the original variable space yields exactly the polyhedron described by the path-modular inequalities. Thus we also show that these inequalities suffice to describe the convex hull of the set of feasible solutions. © 2012 Springer and Mathematical Optimization Society.

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