25 documents found, page 1 of 3
Facility manager perspectives on building condition assessment for Portuguese h...
Matos, Raquel; Rodrigues, Hugo; Costa, Aníbal; Requejo, Cristina; Rodrigues, FernandaThis study aims to provide an overview of the building condition assessment at the facility management stage in higher education buildings in Portugal. A questionnaire survey containing 188 questions was developed and was responded to by experts in the facility management departments of 19 higher education institutions (HEIs) in Portugal. The data analysis, using analytic hierarchy process, showed the difficult...
The shortest path in signed graphs
Costa, Inês Serôdio; Figueiredo, Rosa; Requejo, CristinaThis paper addresses the shortest path problem in a signed graph. Signed graphs are suitable for representing positive/trust and negative/mistrust relationships among the various entities (vertices) of a network. The shortest path in a signed graph can be used to understand how successive relations, even if distant, affect the dynamics of the network. More precisely, the idea is to understand how the relation b...
MIP model-based heuristics for the minimum weighted tree reconstruction problem
Fajarda, Olga; Requejo, CristinaWe consider the Minimum Weighted Tree Reconstruction (MWTR) problem and two matheuristic methods to obtain optimal or near-optimal solutions: the Feasibility Pump heuristic and the Local Branching heuristic. These matheuristics are based on a Mixed Integer Programming (MIP) model used to find feasible solutions. We discuss the applicability and effectiveness of the matheuristics to obtain solutions to the MWTR ...
Weighted iterated local branching for mathematical programming problems with bi...
Rodrigues, Filipe; Agra, Agostinho; Hvattum, Lars Magnus; Requejo, CristinaLocal search algorithms are frequently used to handle complex optimization problems involving binary decision variables. One way of implementing a local search procedure is by using a mixed-integer programming solver to explore a neighborhood defined through a constraint that limits the number of binary variables whose values are allowed to change in a given iteration. Recognizing that not all variables are equ...
Weighted proximity search
Rodrigues, Filipe; Agra, Agostinho; Hvattum, Lars Magnus; Requejo, CristinaProximity search is an iterative method to solve complex mathematical programming problems. At each iteration, the objective function of the problem at hand is replaced by the Hamming distance function to a given solution, and a cutoff constraint is added to impose that any new obtained solution improves the objective function value. A mixed integer programming solver is used to find a feasible solution to this...
Lagrangian duality for robust problems with decomposable functions: the case of...
Rodrigues, Filipe; Agra, Agostinho; Requejo, Cristina; Delage, ErickWe consider a class of min-max robust problems in which the functions that need to be “robustified” can be decomposed as the sum of arbitrary functions. This class of problems includes many practical problems, such as the lot-sizing problem under demand uncertainty. By considering a Lagrangian relaxation of the uncertainty set, we derive a tractable approximation, called the dual Lagrangian approach, that we re...
Temporal constraints and device management for the Skill VRP: mathematical mode...
Cappanera, Paola; Requejo, Cristina; Scutellà, Maria GraziaWe study a generalization of the Skill VRP that incorporates time windows aspects, precedence and synchronization constraints. Specifically, we are given a logistic network where nodes correspond to customers, and where each customer requires a set of (partially ordered) operations. A set of technicians is available to perform such operations, and each technician is qualified to execute only a subset of them, d...
Efficient lower and upper bounds for the weight-constrained minimum spanning tr...
Requejo, Cristina; Santos, EuláliaThe weight-constrained minimum spanning tree problem (WMST) is a combinatorial optimization problem for which simple but effective Lagrangian based algorithms have been used to compute lower and upper bounds. In this work we present several Lagrangian based algorithms for the WMST and propose two new algorithms, one incorporates cover inequalities. A uniform framework for deriving approximate solutions to the W...
Comparing techniques for modelling uncertainty in a maritime inventory routing ...
Rodrigues, Filipe; Agra, Agostinho; Christiansen, Marielle; Hvattum, Lars Magnus; Requejo, CristinaUncertainty is inherent in many planning situations. One example is in maritime transportation, where weather conditions and port occupancy are typically characterized by high levels of uncertainty. This paper considers a maritime inventory routing problem where travel times are uncertain. Taking into account possible delays in the travel times is of main importance to avoid inventory surplus or shortages at th...
A computational comparison of compact MILP formulations for the zero forcing nu...
Agra, Agostinho; Cerdeira, Jorge Orestes; Requejo, CristinaConsider a graph where some of its vertices are colored. A colored vertex with a single uncolored neighbor forces that neighbor to become colored. A zero forcing set is a set of colored vertices that forces all vertices to become colored. The zero forcing number is the size of a minimum forcing set. Finding the minimum forcing set of a graph is NP-hard. We give a new compact mixed integer linear programming for...