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Publications

Publications by CEGI

2019

Optimality in nesting problems: New constraint programming models and a new global constraint for non-overlap

Authors
Cherri, LH; Carravilla, MA; Ribeiro, C; Bragion Toledo, FMB;

Publication
Operations Research Perspectives

Abstract
In two-dimensional nesting problems (irregular packing problems) small pieces with irregular shapes must be packed in large objects. A small number of exact methods have been proposed to solve nesting problems, typically focusing on a single problem variant, the strip packing problem. There are however several other variants of the nesting problem which were identified in the literature and are very relevant in the industry. In this paper, constraint programming (CP) is used to model and solve all the variants of irregular cutting and packing problems proposed in the literature. Three approaches, which differ in the representation of the variable domains, in the way they deal with the core constraints and in the objective functions, are the basis for the three models proposed for each variant of the problem. The non-overlap among pieces, which must be enforced for all the problem variants, is guaranteed through the new global constraint NoOverlap in one of the proposed approaches. Taking the benchmark instances for the strip-packing problem, new instances were generated for each problem variant. Extensive computational experiments were run with these problem instances from the literature to evaluate the performance of each approach applied to each problem variant. The models based on the global constraint NoOverlap performed consistently better for all variants due to the increased propagation and to the low memory usage. The performance of the CP model for the strip packing problem with the global constraint NoOverlap was then compared with the Dotted Board with Rotations using larger instances from the literature. The experiments show that the CP model with global constraint NoOverlap can quickly find good quality solutions in shorter computational times even for large instances. © 2019

2019

Maximizing the expected number of transplants in kidney exchange programs with branch-and-price

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

Publication
Annals of Operations Research

Abstract
In this paper, we propose a branch-and-price approach for solving the problem of maximizing the expected number of transplants in Kidney Exchange Programs (KEPs). In these programs, the decision on which transplants will be conducted is usually made with the support of optimization models with the assumption that all operations will take place. However, after a plan of transplants is defined, a pair may leave the KEP or a more accurate compatibility evaluation exam may invalidate a transplant. To model these possible events we consider probabilities of failure of vertices and of arcs and the objective of maximizing the expected number of transplants. The proposed approach is based on the so-called cycle formulation, where decision variables are associated with cycles. Built on the concept of type of cycle a branch-and-price algorithm is conceived. One subproblem is defined for each type of cycle. We present computational results of the proposed branch-and-price algorithm and compare them with solving directly the cycle formulation (with a general purpose mixed integer programming solver—CPLEX) showing that the proposed approach is the only one suitable for larger instances. © 2017 Springer Science+Business Media, LLC

2019

A multi-objective Monte Carlo tree search for forest harvest scheduling

Authors
Neto, T; Constantino, M; Martins, I; Pedroso, JP;

Publication
European Journal of Operational Research

Abstract

2019

Heuristics for Packing Semifluids

Authors
Pedroso, JP;

Publication
CoRR

Abstract

2019

A service design approach to healthcare innovation: from decision-making to sense-making and institutional change

Authors
Patrício, L; Grenha Teixeira, J; Vink, J;

Publication
AMS Review

Abstract

2019

Bringing service design to the development of health information systems: The case of the Portuguese national electronic health record

Authors
Teixeira, JG; de Pinho, NF; Patricio, L;

Publication
International Journal of Medical Informatics

Abstract
Background: Health Information Systems (HIS), and especially Electronic Health Records (EHR), offer great promise. However, the true benefits of HIS and EHR are more elusive as research shows they have obtained mixed results across countries. To increase the success of these systems while creating value for healthcare professionals, research emphasizes the importance of involving clinical users in the design of HIS. Objective: Following calls for interdisciplinary research and increased end-user participation in HIS development, this paper shows how a service design approach can support the successful development and implementation of national EHRs. Service design brings a human-centered, participatory, holistic, creative and visual approach to HIS development, through an iterative process of exploration, ideation, reflection and implementation, fostering stakeholder participation and co-creation of the solution. Method: This paper presents an in-depth case study of the Portuguese National EHR development and implementation following a service design approach. The study involved individual and group interviews, as well as participatory design workshops with more than 170 participants along the different stages of exploration, ideation, reflection and implementation. Results: The service design approach, including the visual models and tools used across the different design stages, was instrumental to envision new EHR concepts and design the system to enhance healthcare users experience. A qualitative study performed after implementation showed that the EHR was considered useful and easy to use, and these results are backed by widespread usage of the system. Discussion and conclusion: This paper shows how a service design approach can address key challenges in EHR development. By adopting a holistic perspective, service design broadens the scope of EHR development to understand its broader service system and position it to enable value creation with users. The human-centered, participatory, creative, visual and holistic approach supports the understanding of user needs and context, and their active involvement in the design and co-creation effort. This service design approach fosters user adoption at the implementation stage. Service design can thus contribute to the successful development and implementation of EHRs. © 2019 Elsevier B.V.

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