- La Laguna, Tenerife, Canarias, Spain
Abstract Rounding Methods are perturbation techniques used by sta - tistical agencies for protecting privacy when publishing aggregated data like frequency tables Controlled rounding is one of these methods that, besides the possibility... more
Abstract Rounding Methods are perturbation techniques used by sta - tistical agencies for protecting privacy when publishing aggregated data like frequency tables Controlled rounding is one of these methods that, besides the possibility of publishing clearer rounded tables that still re - spect the additivity underlying the original table, also o ers an e ective and powerful way to protect the unsafe data Due to the lack of au - tomatic procedure, it is at present still not used much, and statistical agencies apply less sophisticated variants (e g , random rounding) which have several disadvantages This work presents an automatic procedure to apply Controlled Rounding in a simple and friendly way on a per - sonal computer The tool is written in C programming language, using Excel SDK - API, and is implemented as an add - in for Microsoft Excel - a standard software we chose due to its wide spread on many personal computers and because of its familiarity to many users who work with tabular material in statistical agencies The algorithm is based on solv - ing an integer linear program in order to find a "good" rounded table while ensuring additivity and protection, as recently proposed by the first author An extra feature of the here - presented implementation is that it does not need to be linked with a commercial mathematical pro - gramming software; better performance on large scale tables would be obtained when Xpress or Cplex is available on the computer
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CORAL 2003, a Conference on Routing and Location, was held in Puerto de la Cruz (Tenerife, Spain) from February 24-26, 2003.A wonderful place, close to the black sand of the beach, and a nice temperature welcomed a group of senior and... more
CORAL 2003, a Conference on Routing and Location, was held in Puerto de la Cruz (Tenerife, Spain) from February 24-26, 2003.A wonderful place, close to the black sand of the beach, and a nice temperature welcomed a group of senior and young researchers from Canada, England, France, Germany, and Spain. Social activities were also provided and sponsored by the Cabildo
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ABSTRACT We study the hub location and routing problem where we decideon the location of hubs, the allocation of nodes to hubs, and the routing among the nodes allocated to the same hubs, with the aim of minimizing the total... more
ABSTRACT We study the hub location and routing problem where we decideon the location of hubs, the allocation of nodes to hubs, and the routing among the nodes allocated to the same hubs, with the aim of minimizing the total transportation cost. Each hub has one vehicle that visits all the nodes assigned to it on a cycle. We propose a mixed integer programming formulation for this problem and strengthen it with valid inequalities. We devise separation routines for these inequalities and develop a branch-and-cut algorithm which is tested on CAB and AP instances from the literature. The results show that the formulation is strong and the branch-and-cut algorithm is able to solve instances with up to 50 nodes.
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Abstract. This paper addresses a capacitated hub problem consisting of choosing the routes and the hubs to use in order to send a set of commodities from sources to destinations in a given capacitated network with minimum cost. The... more
Abstract. This paper addresses a capacitated hub problem consisting of choosing the routes and the hubs to use in order to send a set of commodities from sources to destinations in a given capacitated network with minimum cost. The capacities and costs of the arcs and hubs ...
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Controlled Rounding is a technique to replace each cell value in a table with a multiple of a base number such that the new table satisfies the same equations as the original table. Statistical agencies prefer a solution where cell values... more
Controlled Rounding is a technique to replace each cell value in a table with a multiple of a base number such that the new table satisfies the same equations as the original table. Statistical agencies prefer a solution where cell values already multiple of the base number remain unchanged, while the others are one of the two closest multiple of the base number (i.e., rounded up or rounded down). This solution is called zero-restricted rounding. Finding such a solution is a very complicated problems, and on some tables it may not exist. This paper presents a mathematical model and an algorithm to find a good-enough near-feasible solution for tables where a zero-restricted rounding is complicated. It also presents computational results showing the behavior of the proposal in practice.
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Confirming statistical confidentiality as vital to the stewardship of personal data, the United Nations set out Principle 6 of its Fundamental Principles of Official Statistics: Individual data collected by statistical agencies for... more
Confirming statistical confidentiality as vital to the stewardship of personal data, the United Nations set out Principle 6 of its Fundamental Principles of Official Statistics: Individual data collected by statistical agencies for statistical compilation, whether they refer to natural or legal persons, are to be strictly confidential and used exclusively for statistical purposes. Data stewardship is active on two fronts:
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ABSTRACT The Vehicle Routing Problem with a minimum number of customers per route concerns the Capacitated Vehicle Routing Problem with unit-demand customers and a lower bound on the number of customers visited by each vehicle. This paper... more
ABSTRACT The Vehicle Routing Problem with a minimum number of customers per route concerns the Capacitated Vehicle Routing Problem with unit-demand customers and a lower bound on the number of customers visited by each vehicle. This paper answers two open questions in the article (Gouveia et al., in press) [5]: finding a compact formulation for the problem such that the corresponding linear programming relaxation implies the Enhanced Reverse Multistar inequalities, and finding a polynomial-time separation algorithm for this class of inequalities.
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... Juan-José Salazar-González Departamento de Estadística, Investigación Operativa y Computación, Universidad de La Laguna, Av. ... In this article we aim at determining the PT of a set of n taxa given the knowledge of a n × n symmetric... more
... Juan-José Salazar-González Departamento de Estadística, Investigación Operativa y Computación, Universidad de La Laguna, Av. ... In this article we aim at determining the PT of a set of n taxa given the knowledge of a n × n symmetric dis-tance matrix D = {dij} of estimated ...
Research Interests: Bioinformatics, Applied Mathematics, Molecular Biology, Modeling, Networks, and 12 moreDistributed System, Phylogeny, Network Design, Mathematical Model, Branch and Bound, Protein Sequence Analysis, Mixed Integer Programming, Phylogenetic Tree, Numerical Analysis and Computational Mathematics, Lower Bound, Phylogenetic Reconstruction, and DNA sequence
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ABSTRACT Port infrastructure has characteristics that are classified by quasifixed inputs, meaning they cannot be immediately adjusted, contributing to the production of transport services over long periods of time. Another important... more
ABSTRACT Port infrastructure has characteristics that are classified by quasifixed inputs, meaning they cannot be immediately adjusted, contributing to the production of transport services over long periods of time. Another important characteristic of port infrastructure is that its current technology is a consequence of investment decisions made in the past and whose effects resonate over various periods. A dynamic approach that acknowledges the inter-temporal relationship between the inputs used and the resulting outputs is more adequate to handle this type of inputs. In this paper, the efficiency achieved for Spanish Port Authorities from 2000 to 2007 has been obtained using a dynamic inter-temporal Data Envelopment Analysis cost model, obtaining dynamic and static components of inefficiency. The result has been compared with that obtained from a static approach, showing that the static model overstates all components of cost inefficiency. Moreover, since by its very nature the static model is unable to yield the dynamic inefficiency, it has a tendency to transform efficiency into technical and allocative ones, which can lead to faulty investment decisions. If we do not consider the specific characteristics of the port infrastructure, the consequences could lead to investment decisions being made that seek to expand the productive capacity of the port when such an expansion is not warranted.
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Research Interests: Information Systems, Marketing, Optimization (Mathematical Programming), Computer Science, Information Technology, and 22 moreProject Management, Combinatorial Optimization, Operations Research, Production, Telecommunications, Logistics, Mathematical Programming, Routing, Management Science, Forecasting, Scheduling, Telecommunication, Operational Research, Optimization, Optimization Problem, Investment, Mathematical Sciences, Reliability, The, Location, Communications Technology, and Location Problem
Page 1. VI Congreso Galego de Estatıstica e Investigación de Operacións Vigo 5–7 de Novembro de 2003 NEW ALGORITHMS FOR THE EDITING AND IMPUTATION PROBLEM Jorge Riera Ledesma and Juan José Salazar González. ...
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ABSTRACT This paper addresses an extension of the Traveling Salesman Problem where a vehicle with a limited capacity must transport commodities. Each commodity has a weight, and exactly one origin and one destination. The objective is to... more
ABSTRACT This paper addresses an extension of the Traveling Salesman Problem where a vehicle with a limited capacity must transport commodities. Each commodity has a weight, and exactly one origin and one destination. The objective is to find a minimum length Hamiltonian tour satisfying all the transportation requests without ever violating the capacity constraint. We propose for this problem a hybrid heuristic approach that combines the GRASP and VND metaheuristic techniques. Two variants of the method are presented, one of them using a mathematical programming based local search. We conduct computational experiments to compare the developed algorithms. The experiments show that they improve the best known solutions for a set of instances from the literature, and are able to cope with instances with up to 300 customers and 600 commodities in a reasonable amount of computation time.
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ABSTRACT Aphylogeny is an unrooted binary tree that represents the evolutionary relationships of a set of n species. Phylogenies find applications in several scientific areas ranging from medical research, to drug discovery, to... more
ABSTRACT Aphylogeny is an unrooted binary tree that represents the evolutionary relationships of a set of n species. Phylogenies find applications in several scientific areas ranging from medical research, to drug discovery, to epidemiology, to systematics, and to population dynamics. In such applications, the available information is usually restricted to the leaves of a phylogeny and is represented by molecular data extracted from the analyzed species, such as DNA, RNA, amino acid, or codon fragments. On the contrary, the information about the phylogeny itself is generally missing and is determined by solving an optimization problem, called the phylogeny estimation problem (PEP), whose versions depend on the criterion used to select a phylogeny from among plausible alternatives. In this paper, we investigate a recent version of the PEP, called the balanced minimum evolution problem (BMEP). We present a mixed-integer linear programming model to exactly solve instances of the BMEP and develop branching rules and families of valid inequalities to further strengthen the model. Our results give perspective on the mathematics of the BMEP and suggest new directions on the development of future efficient exact approaches to solutions of the problem.
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The job Sequencing and tool Switching Problem (SSP) involves optimally sequencing jobs and assigning tools to a capacitated magazine in order to minimize the number of tool switches. This article analyzes two integer linear programming... more
The job Sequencing and tool Switching Problem (SSP) involves optimally sequencing jobs and assigning tools to a capacitated magazine in order to minimize the number of tool switches. This article analyzes two integer linear programming formulations for the SSP. A ...
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Page 1. 1 MEASUREMENT EFFICIENCY AND RETURNS TO SCALE WITH QUASIFIXED INPUTS: AN APPLICATION OF DYNAMIC DEA TO INFRASTRUCTURE SERVICES IN SPANISH PORTS Juan José Díaz-Hernández 1a Eduardo Martínez-Budría b ...
ABSTRACT This paper presents a new combinatorial optimization problem that can be used to model the deployment of broadband telecommunications systems in which optical fiber cables are installed between a central office and a number of... more
ABSTRACT This paper presents a new combinatorial optimization problem that can be used to model the deployment of broadband telecommunications systems in which optical fiber cables are installed between a central office and a number of end-customers. In this capacitated network design problem the installation of optical fiber cables with sufficient capacity is required to carry the traffic from the central office to the end-customers at minimum cost. In the situation motivating this research the network does not necessarily need to connect all customers (or at least not with the best available technology). Instead, some nodes are potential customers. The aim is to select the customers to be connected to the central server and to choose the cable capacities to establish these connections. The telecom company takes the strategic decision of fixing a percentage of customers that should be served, and aims for minimizing the total cost of the network providing this minimum service. For that reason the underlying problem is called the Prize-Collecting Local Access Network Design problem (PC-LAN). We propose a branch-and-cut approach for solving small instances. For large instances of practical importance, our approach turns into a mixed integer programming (MIP) based heuristic procedure which combines the cutting-plane algorithm with a multi-start heuristic algorithm. The multi-start heuristic algorithm starts with fractional values of the LP-solutions and creates feasible solutions that are later improved using a local improvement strategy. Computational experiments are conducted on small instances from the literature. In addition, we introduce a new benchmark set of real-world instances with up to 86,000 nodes, 116,000 edges and 1500 potential customers. Using our MIP-based approach we are able to solve most of the small instances to proven optimality. For more difficult instances, we are not only able to provide high-quality feasible solutions, but also to provide certificate on their quality by calculating lower bounds to the optimal solution values.
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This article introduces a new problem called Steiner cycle problem (SCP), closely related to the widely-studied travelling salesman problem (TSP) and the Steiner tree problem. Given an undirected graph G with a penalty associated to each... more
This article introduces a new problem called Steiner cycle problem (SCP), closely related to the widely-studied travelling salesman problem (TSP) and the Steiner tree problem. Given an undirected graph G with a penalty associated to each node and a cost to each edge, and given a subset of nodes W, the problem consists on finding a simple cycle in G visiting at least the nodes in W and minimizing the sum of the costs of edges in the cycle plus the penalties of nodes not in the cycle. This problem finds applications in the optimal design of telecommunication systems, and generalizes the known TSP and the weighted Girth problem. We analyze the polyhedral structure associated to the SCP introducing two lifting procedures to extend facet-defining inequalities from the travelling salesman polytope. The obtained results can be applied to the weighted Girth problem. Moreover, they can also be used in a cutting-plane approach to solve the SCP.
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In this paper we show and discuss a family of inequalities for solving a variant of the classical vehicle routing problem where also a lower bound is considered. The inequalities are related to the projected inequalities from a single... more
In this paper we show and discuss a family of inequalities for solving a variant of the classical vehicle routing problem where also a lower bound is considered. The inequalities are related to the projected inequalities from a single commodity flow formulation. Other inequalities are based on rounding procedures. We also show computational experiments proving the utility of the new inequalities.