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Publications

Publications by Xenia Klimentova

2015

A compact formulation for maximizing the expected number of transplants in kidney exchange programs

Authors
Alvelos, F; Klimentova, X; Rais, A; Viana, A;

Publication
MINI EURO CONFERENCE ON IMPROVING HEALTHCARE: NEW CHALLENGES, NEW APPROACHES

Abstract
Kidney exchange programs (KEPs) allow the exchange of kidneys between incompatible donor-recipient pairs. Optimization approaches can help KEPs in defining which transplants should be made among all incompatible pairs according to some objective. The most common objective is to maximize the number of transplants. In this paper, we propose an integer programming model which addresses the objective of maximizing the expected number of transplants, given that there are equal probabilities of failure associated with vertices and arcs. The model is compact, i.e. has a polynomial number of decision variables and constraints, and therefore can be solved directly by a general purpose integer programming solver (e.g. Cplex).

2016

Maximising expectation of the number of transplants in kidney exchange programmes

Authors
Klimentova, X; Pedroso, JP; Viana, A;

Publication
Computers & OR

Abstract
This paper addresses the problem of maximising the expected number of transplants in kidney exchange programmes. New schemes for matching rearrangement in case of failure are presented, along with a new tree search algorithm used for the computation of optimal expected values. Extensive computational experiments demonstrate the effectiveness of the algorithm and reveal a clear superiority of a newly proposed scheme, subset-recourse, as compared to previously known approaches.

2014

A New Branch-and-Price Approach for the Kidney Exchange Problem

Authors
Klimentova, X; Alvelos, F; Viana, A;

Publication
COMPUTATIONAL SCIENCE AND ITS APPLICATIONS - ICCSA 2014, PT II

Abstract
The kidney exchange problem (KEP) is an optimization problem arising in the framework of transplant programs that allow exchange of kidneys between two or more incompatible patient-donor pairs. In this paper an approach based on a new decomposition model and branch-and-price is proposed to solve large KEP instances. The optimization problem considers, hierarchically, the maximization of the number of transplants and the minimization of the size of exchange cycles. Computational comparison of different variants of branch-and-price for the standard and the proposed objective functions are presented. The results show the efficiency of the proposed approach for solving large instances.

2018

Observability of power systems with optimal PMU placement

Authors
Carvalho, M; Klimentova, X; Viana, A;

Publication
Computers & Operations Research

Abstract

2013

New insights on integer-programming models for the kidney exchange problem

Authors
Constantino, M; Klimentova, X; Viana, A; Rais, A;

Publication
EUROPEAN JOURNAL OF OPERATIONAL RESEARCH

Abstract
In recent years several countries have set up policies that allow exchange of kidneys between two or more incompatible patient-donor pairs. These policies lead to what is commonly known as kidney exchange programs. The underlying optimization problems can be formulated as integer programming models. Previously proposed models for kidney exchange programs have exponential numbers of constraints or variables, which makes them fairly difficult to solve when the problem size is large. In this work we propose two compact formulations for the problem, explain how these formulations can be adapted to address some problem variants, and provide results on the dominance of some models over others. Finally we present a systematic comparison between our models and two previously proposed ones via thorough computational analysis. Results show that compact formulations have advantages over non-compact ones when the problem size is large.

2016

Maximizing expected number of transplants in kidney exchange programs

Authors
Alvelos, F; Klimentova, X; Rais, A; Viana, A;

Publication
Electronic Notes in Discrete Mathematics

Abstract
In this paper we address the problem of maximizing the expected number of transplants in a kidney exchange program. We propose an integer programming model with an exponential number of decision variables which are associated with cycles. By introducing the concept of type of cycle, we avoid the complete cycle enumeration and develop a branch-and-price approach. © 2016 Elsevier B.V.

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