Luciana S. Buriol

Universidade Federal do Rio Grande do Sul | UFRGS · Departamento de Informática Teórica

Pattern databases have been successfully applied to several problems. Their use assumes that the goal state is known, and once the pattern database is built, commonly it can be used by all instances. However, in Sokoban, before solving the puzzle, the goal position of each stone is unknown. Moreover, each Sokoban instance has its own state space se...

This paper presents an integer programming model and a matheuristic for the physician rostering problem. Constraints related to physician’s preferences, legal restrictions, hospital requirements and workload balance are investigated. Moreover, a comparison of physician and nurse rostering is analyzed to identify common constraints present in both p...

Cloud computing has emerged as a new paradigm for hosting and supplying services over the Internet. This technology has brought many benefits, such as eliminating the need for maintaining expensive computing hardware. With an increasing demand for cloud computing, providing performance guarantees for applications that run over cloud become importan...

This work presents an empirical analysis of exact algorithms for the unbounded knapsack problem, which includes seven algorithms from the literature, two commercial solvers, and more than ten thousand instances. The terminating step-off, a dynamic programming algorithm from 1966, presented the lowest mean time to solve the most recent benchmark fro...

In this work, the Pickup and Delivery Problem with Time Windows is studied. It is a combinatorial optimization problem, in which the objective is to construct the best set of vehicle routes while respecting side constraints, such as precedence between locations to be visited, and the time to service them. To tackle this problem, a matheuristic base...

This work presents a Relax-and-Fix algorithm to solve a class of single product Maritime Inventory Routing Problems. The problem consists of routing and scheduling a heterogeneous fleet of vessels to supply a set of ports, respecting lower and upper limits of inventory at production and consumption ports, along with a time horizon. A fixed charge n...

Several real-world problems can be modeled as graph problems. Graph algorithms and theories that have evolved for decades can be applied to solve the problem on hand. Interestingly, many of these graph problems can be solved polynomially, while small changes in a problem definition turn the problem difficult. In this chapter, we explore this path f...

Nesse resumo extendido nós apresentamos o UKP5, um algoritmo para solucionar o unbounded knapsack problem (problema da mochila com repetições). O UKP5 é baseado em programação dinâmica, mas implementado de uma forma não-tradicional: ao invés de olhar para trás para usar soluções de subproblemas previamente computados, ele armazena limites inferiore...

While Network Function Virtualization (NFV) is increasingly gaining momentum, with promising benefits of flexible service function deployment and reduced operations and management costs, there are several challenges that remain to be properly tackled, so that it can realize its full potential. One of these challenges, which has a significant impact on...

Network virtualization is a growing trend in the implementation of Internet infrastructures. The Virtual Network Embedding problem is one of the challenges in the virtualization of physical networks. This work shows that finding a feasible solution to this problem is NP-Hard. However, in practice, it can be solved to optimality by exploiting the pr...

This work presents a Branch-and-Price algorithm for solving a compressor scheduling problem with applications in oil production. The problem consists in defining a set of compressors to be installed for supplying the gas-lift demand of oil wells while minimizing the associated costs. Owing to the non-convex nature of the objective function, two pie...

This work presents a relax-and-fix algorithm for solving a class of single product Maritime Inventory Routing Problem. The problem consists in routing and scheduling a heterogeneous fleet of vessels to supply a set of ports, keeping inventory at production and consumption ports between lower and upper limits. Two sets of constraints are proposed bo...

Moving-blocks problems are extremely hard to solve and a representative abstraction of many applications. Despite their importance, the known computational complexity results are limited to few versions of these problems. In addition, there are no effective methods to optimally solve them. We address both of these issues. This thesis proves the PSP...

Population growth and the massive production of automotive vehicles have lead to the increase of traffic congestion problems. Traffic congestion today is not limited to large metropolitan areas, but is observed even in medium-sized cities and highways. Traffic engineering can contribute to lessen these problems. One possibility, explored in this pa...

School timetabling is a classic optimization problem that has been extensively studied due to its practical and theoretical importance. It consists in scheduling a set of class-teacher meetings in a predetermined period of time, satisfying requirements of different types. Given the combinatorial nature of this problem, solving medium and large inst...

In this paper we present UKP5, a novel algorithm for solving the unbounded knapsack problem. UKP5 is based on dynamic programming, but implemented in a non traditional way: instead of looking backward for stored values of subproblems, it stores incremental lower bounds forward. UKP5 uses sparsity, periodicity, and dominance for speeding up computat...

We prove PSPACE-completeness of a broad class of moving-blocks problems similar to the well-known puzzle Sokoban. Several computational complexity results are known for moving-blocks problems. However, most of the literature is focused on problems with push moves and the complexity of many of them are still open. In this article, we study the compu...

Network virtualization has become increasingly popular in recent years. It has the potential to allow timely handling of network infrastructure requests and, after instantiated, their lifecycle. In addition, it enables improved physical resource utilization. However, the use of network virtualization in large-scale, real environments depends on the...

A pattern database (PDB) stores shortest distances from abstract states to a set of abstract goal states. For many search problems the best heuristic function is obtained using PDBs. We aim to find optimal solutions for Sokoban using PDBs. Due to the domain-specific characteristics of the goal states a straightforward application of PDBs in Sokoban...

The Compressor Scheduling Problem (CSP) can be considered a variation of the classical Capacitated Facility Location Problem, with two types of demands and capacities (gas rate and gas pressure). In the CSP, the objective is to minimize the compressors installation cost and the main-tenance/energy loss in the pipeline between all wells and the inst...

Cloud computing has recently emerged as a new technology for hosting and supplying services over the Internet. With an increasing demand for cloud computing, providing performance guarantees for applications that run over cloud become important. Applications can be abstracted into a set of virtual machines with certain guarantees depicting the qual...

Cloud computing has recently emerged as a new technology for hosting and supplying services over the Internet. This technology has brought many benefits, such as eliminating the need for maintaining expensive computing hardware and allowing business owners to start from small and increase resources only when there is a rise in service demand. With...

Network Function Virtualization (NFV) is a promis- ing network architecture concept, in which virtualization tech- nologies are employed to manage networking functions via software as opposed to having to rely on hardware to handle these functions. By shifting dedicated, hardware-based network function processing to software running on commoditized...

Given an initial assignment of processes to machines, the machine reassignment problem is to find an assignment that improves the machine usage, subject to several resource and allocation constraints, and considering reassignment costs. We propose a heuristic based on simulated annealing for solving this problem. It uses two neighborhoods, one that...

A long standing problem in structural bioinformatics is to determine the three-dimensional (3-D) structure of a protein when only a sequence of amino acid residues is given. Many computational methodologies and algorithms have been proposed as a solution to the 3-D Protein Structure Prediction (3-D-PSP) problem. These methods can be divided in four...

A geração de quadro de horários para universidades é um problema clássico de otimização combinatória que leva em consideração um grande número de variáveis e requisitos. Este tipo de problema em geral contém restrições específicas da aplicação, gerando uma grande quantidade de variações do problema. Apesar do problema ser NP-Completo, o mesmo é res...

The high school timetabling is a classical combinatorial optimization problem that takes a large number of variables and constraints into account. Due to its combinatorial nature, solving medium and large instances to optimality is a challenging task. When resources are tight, it is often difficult to find even a feasible solution. Among the differ...

Network virtualization has become increasingly popular in recent years. It has the potential to allow timely handling of network infrastructure requests and, after instantiated, their lifecycle. In addition, it enables improved physical resource utilization. However, the use of network virtualization in large-scale, real environments depends on the...

One of the research challenges approached recently in the literature is the efficient mapping of virtual networks on top of physical infrastructures. Although there have been efforts to solve it, we observe that a number of virtual network requests are rejected due to the exhaustion of resources only in key points of the infrastructure. In this pap...

The prediction and analysis of the three- dimensional (3D) structure of proteins is a key research problem in Structural Bioinformatics. The 1990’s Genome Projects resulted in a large increase in the number of available protein sequences. However, the number of identified 3D protein structures have not followed the same growth trend. Currently, the...

One of the research challenges approached in recent literature is the efficient mapping of virtual networks on top of physical infrastructures. Although there have been efforts to solve it, we observe that a number of vir- tual network requests are rejected due to the exhaustion of resources only in key points of the infrastructure. In this paper,...

Network virtualization is a mechanism that allows the coexistence of multiple virtual networks on top of a single physical substrate. One of the research challenges addressed recently in the literature is the efficient mapping of virtual resources on physical infrastructures. Although this challenge has received considerable attention, state-of-the...

Pattern databases have been successfully applied to several problems. Their use assumes that the goal state is known, and once the pattern database is built, commonly it can be used by all instances. However, in Sokoban, before solving the puzzle, the goal position of each stone is unknown. Moreover, each Sokoban instance has its own state space se...

Three-dimensional (3-D) protein structure determination has become an important area of research in structural bioinformatics. Proteins are responsible for the execution of different functions in the cell. Understanding the 3-D structure provides important information about the protein function. Many computational methodologies for the protein stru...

Although network virtualization can improve security by isolating traffic from different networks, routers and links are still vulnerable to attacks on the underlying network. High capacity physical links, in particular, constitute good targets since they may be important for a large number of virtual networks. Previous work protects virtual networ...

Cloud computing can offer virtually unlimited re- sources without any upfront capital investment through a pay-per-use pricing model. However, the shared nature of multi-tenant cloud datacenter networks enables unfair or malicious use of the intra-cloud network by tenants, allowing attacks against the privacy and integrity of data and the availabil...

Network virtualization can potentially limit the impact of attacks by isolating traffic from different networks. However, routers and links are still vulnerable to attacks on the underlying network. Specifically, should a physical link be compromised, all embedded virtual links will be affected. Previous work protects virtual networks by setting as...

One of the main research problems in structural bioinformatics is the prediction of three-dimensional structures (3-D) of polypeptides or proteins. The current rate at which amino acid sequences are identified increases much faster than the 3-D protein structure determination by experimental methods, such as X-ray diffraction and NMR techniques. Th...

Multi-objective Ant Colony Optimization (MOACO) algorithms have been successfully applied to several multi-objective combinatorial optimization problems (MCOP) over the past decade. Recently, we proposed a MOACO algorithm named GRACE for the multi-objective shortest path (MSP) problem, confirming the efficiency of such metaheuristic for this MCOP....

Network virtualization is a mechanism that allows the coexistence of multiple virtual networks on top of a single physical substrate. One of the re- search challenges addressed in the literature is the efficient mapping of virtual resources on physical infrastructures. Although this challenge has received con- siderable attention, state-of-the-art...

Pattern databases have been successfully applied to several problems. Their use assumes that the goal state is known, and once the pattern database is built, commonly it can be used by all instances. However, in Sokoban, before solving the puzzle, the goal position of each stone is unknown. Moreover, each Sokoban instance has its own state space se...

Network virtualization enables the creation of multiple instances of virtual networks on top of a single physical infrastructure. Given its wide applicability, this technique has attracted a lot of interest both from academic researchers and major companies within the segment of computer networks. Although recent efforts (motivated mainly by the se...

The school timetabling is a classic optimization problem that takes a large number of variables and constraints into account. Due to the combinatorial nature of this problem, it is very difficult to solve it manually and is often difficult to find a feasible solution when resources are tight. Among the different requirements that are considered in...

Cellular automata models for traffic movement assume that vehicles are particles without routes. However, if one is interested in analysing microscopic properties, it is necessary to assign a route to each trip. This pa-per discusses the latest developments in the ITSUMO traffic simulator. These developments aim at modeling more sophisticated drive...

One of the main research problems in Structural Bioinformatics is related to the prediction of three-dimensional structures (3-D) of polypeptides or proteins. The rate at which amino acid sequences are identified is increasing faster than the 3-D protein structure determination by experimental methods. Computational prediction methods have been dev...

The use of metaheuristics in Multi-objective Combinatorial Optimization, particularly Ant Colony Optimization (ACO), has grown recently. This paper proposes an approach where multi-species ants compete for food resources. Each species has its own search strategy and do not access pheromone information of other species. As in nature, successful ant...

The Multi-objective Shortest Path Problem (MSP) is a widely studied NP-Hard problem. A few exact algorithms were already proposed to solve this problem, however none is able to solve large instances with three or more objectives. Recently, some metaheuristics have been proposed for the MSP, but little can be said about their efficiency regarding ea...

The impact of the web as source of information and services is growing continuously and consequently the importance of appropriate design of algorithms for the web has increased. Such algorithms depend both on the web structure and how it evolves over time. The webgraph is formed by the link structure of webpages. It is well known that this graph i...

One of the main research problems in Structural Bioinformatics is the analysis and prediction of three-dimensional structures (3-D) of polypeptides or proteins. The 1990's Genome projects resulted in a large increase in the number of protein sequences. However, the number of identified 3-D protein structures has not followed the same trend. The det...

We study the effect of perturbations on the Price of Anarchy for the Traffic Assignment Problem. Adopting the smoothed analysis approach, we randomly perturb the latency functions of the given network and estimate the expected Price of Anarchy on the perturbed instances. We provide both theoretical and experimental results that show that the Smooth...

One of the main goals in transportation planning is to achieve solutions for two classical problems, the traffic assignmentand toll pricing problems. The traffic assignment problem aims to minimize total travel de- lay among all travelers. Based on data derived from the first problem, the toll pricing problem determines the set of tolls and corresp...

Abstract Interior gateway routing protocols like Open Shortest Path First (OSPF) and Distributed Exponentially Weighted Flow Splitting (DEFT) send flow through forward links toward the destination node. OSPF routes only on shortest-weight paths, whereas DEFT sends flow on all forward links, but with an exponential penalty on longer paths. Finding s...

Interior gateway routing protocols like OSPF (Open Shortest Path First) and DEFT (Distributed Exponentially-Weighted Flow Splitting) send flow through forward links towards the destination node. OSPF routes only on shortest-weight paths, whereas DEFT sends flow on all forward links, but with an exponential penalty on longer paths. Finding suitable...

One of the main goals in a transportation planning process is to achieve solutions for two classical problems: the traffic assignment problem, which minimizes the total travel delay among all trav-elers, and the toll pricing problem which settles, based on data derived from the first problem, the tolls that would collectively benefit all travelers...

Resumo Este artigo apresenta um algoritmo de busca tabu para o problema de roteamento de veículos capacita-dos com restri oes de empacotamento tridimensionais (3D-Loading Capacitated Vehicle Routing Problem – 3L-CVRP). Existem diversas propostas na literatura para solucionar o empacotamento em duas e três dimensões, assim como diversas voltadas par...

We study the problem of allocating automatic switches in electrical networks in order to improve their reliability. Our approach combines the solution of the switch allocation problem with the related subproblem of optimal network reconfiguration. This paper presents a GRASP for solving this joint problem, as well as a faster method for the evaluat...

Dynamic shortest path algorithms update the shortest paths to take into ac-count a change in an edge weight. This paper describes a new technique that allows the reduction of heap sizes used by several dynamic shortest path algorithms. For unit weight change, the updates can be done without heaps. These reductions almost always reduce the computati...

We present random sampling algorithms that with probability at least 1 − δ compute a (1 ±ε)-approximation of the clustering coefficient and of the number of bipartite clique subgraphs of a graph given as an incidence stream of edges. The space used by our algorithm to estimate the clustering coefficient is inversely related to the clustering coeffi...

A wireless sensor network (WSN) is energy constrained, and the extension of its lifetime is one of the most important issues in its design. Usually, a WSN collects a large amount of data from the environment. In contrast to the conventional remote sensing - based on satellites that collect large images, sound files, or specific scientific data - se...

This work presents a sampling data stream algorithm for wireless sensor networks (WSNs). The proposed algorithm is based on sampling techniques applied to data histograms created from original data streams acquired by sensor nodes. As a result, the algorithm provides a sample of only log n items to represent the original data of n elements. We show...

Internet protocol (IP) traffic follows rules established by routing protocols. Shortest path-based protocols, such as Open Shortest Path First (OSPF), direct traffic based on arc weights assigned by the network operator. Each router computes shortest paths and creates destination tables used for routing flow on the shortest paths. If a router has m...

Internet protocol (IP) traffic follows rules established by routing protocols. Shortest path-based protocols, such as Open Shortest Path First (OSPF), direct traffic based on arc weights assigned by the network operator. Each router computes shortest paths and creates destination tables used for routing flow on the shortest paths. If a router has m...

To use interior gateway protocols like OSPF (Open Shortest Path First, (6)), IS-IS (Intermediate System- Intermediate System), and DEFT (Distributed Exponentially-weighted Flow Splitting, (7)) it is necessary to set the link weights to allow data routing. The problem of finding suitable weights for these protocols is known as the weight setting pro...

Wikipedia is an online encyclopedia, available in more than 100 languages and comprising over 1 million articles in its English version. If we consider each Wikipedia article as a node and each hyperlink between articles as an arc we have a "Wikigraph", a graph that represents the link structure of Wikipedia. The Wikigraph differs from other Web gr...

For UFRGS's first participation on CLEF our goal was to compare the performance of heavier and lighter stemming strateg ies using the Portuguese data collections for Monolingual Ad-hoc retrieval. The results show that the safest strategy was to use the lighter alternative (reducing plural forms only). On a query-by-query analysis, full stemming ach...