Search results for "Tabu"
showing 10 items of 180 documents
Context-Independent Scatter and Tabu Search for Permutation Problems
2005
In this paper, we develop a general-purpose heuristic for permutations problems. The procedure is based on the scatter-search and tabu-search methodologies and treats the objective-function evaluation as a black box, making the search algorithm context-independent. Therefore, our main contribution consists of the development and testing of a procedure that uses no knowledge from the problem context to search for the optimal solution. We perform computational experiments with four well-known permutation problems to study the efficiency and effectiveness of the proposed method. These experiments include a comparison with two commercially available software packages that are also based on met…
Heuristics for the bandwidth colouring problem
2010
The bandwidth colouring problem consists of assigning a colour to each vertex of a graph, so that the absolute value of the difference between the colours of adjacent vertices is at least the value of the weight of the associated edge. This problem generalises the classical vertex colouring problem and different heuristics have recently been proposed to obtain high quality solutions. In this paper we describe both memory-based and memory-less methods to solve the bandwidth colouring problem. In particular we propose new constructive and improvement methods based on tabu search and GRASP. Comparison of our results with previously reported instances and existing heuristics indicate that the m…
Designing portfolios of financial products via integrated simulation and optimization models
1999
We analyze the problem of debt issuance through the sale of innovative financial products. The problem is broken down to questions of designing the financial products, specifying the debt structure with the amount issued in each product, and determining an optimal level of financial leverage. We formulate a hierarchical optimization model to integrate these three issues and provide constructive answers. Input data for the models are obtained from Monte Carlo simulation procedures that generate scenarios of holding period returns of the designed products. The hierarchical optimization model is specialized for the problem of issuing a portfolio of callable bonds to fund mortgage assets. The …
Scatter Search and Path Relinking: Advances and Applications
2006
Scatter search (SS) is a population-based method that has recently been shown to yield promising outcomes for solving combinatorial and nonlinear optimization problems. Based on formulations originally proposed in the 1960s for combining decision rules and problem constraints, SS uses strategies for combining solution vectors that have proved effective in a variety of problem settings. Path relinking (PR) has been suggested as an approach to integrate intensification and diversification strategies in a search scheme. The approach may be viewed as an extreme (highly focused) instance of a strategy that seeks to incorporate attributes of high quality solutions, by creating inducements to favo…
Resource-constrained project scheduling: A critical activity reordering heuristic
2003
Abstract In this paper, we present a new metaheuristic algorithm for the resource-constrained project-scheduling problem. The procedure is a non-standard implementation of fundamental concepts of tabu search without explicitly using memory structures embedded in a population-based framework. The procedure makes use of a fan search strategy to intensify the search, whereas a strategic oscillation mechanism loosely related to the forward/backward technique provides the necessary diversification. Our implementation employs the topological order (TO) representation of schedules. To explore the TO vector space we introduce three types of moves, two of them based on the concept of relative critic…
Intertextualidad y metaficción en Trazo de tiza de Miguelanxo Prado
2009
Este artículo desarrolla el análisis de la obra Trazo de tiza (Prado, 1993) del ilustrador y autor de cómics Miguelanxo Prado, que obtuvo los premios “Alph-Art al Mejor Álbum Extranjero” en el Festival del Cómic de Angoulême en 1994 y el de “Mejor obra” en el Saló Internacional del Còmic de Barcelona de 1994. En primer lugar se centrará la atención en la explícita red intertextual que la obra plantea: la estructura narrativa de Trazo de tiza surge a partir de una reflexión extraída del cuento de Jorge Luis Borges “Tlön, Uqbar, Orbis Tertius” (Ficciones, 1944). El entramado se completa con otros dos textos: La invención de Morel, novela de Bioy Casares, y Dama de Porto Pim, libro de relatos …
The Artek cup for total hip replacement of dysplastic hip joints.
2003
One specific difficulty in total hip replacement for developmental dysplasia of the hip is a shallow acetabulum with a short anteroposterior diameter. In a prospective cohort study we investigated the short-term results of the Artek cup, designed with a shallow outline and a height-reduced metal inlay for a large size 38 mm metal head, in a group of female patients with mild dysplasia of the hip.Fourteen consecutive patients with 17 dysplastic hip joints were included in the study. Their average age was 42 years. Fourteen hips had dysplasia Crowe grade I; 3 hips had dysplasia Crowe grade II. The femoral head centre was localized according to Pagnano in zone 1 in 3 cases, in zone 3 in 6 case…
Scatter Search—Wellsprings and Challenges
2006
I came up with the idea of editing this volume in the summer of 2002 while working on the book "Scatter search methodologies and implementations in C" with Manuel Laguna in the University of Colorado at Boulder. There, Fred Glover kindly let me use his office, where I found a copy of the "Tabu Search Methods for Optimization" special issue that he edited in 1988 for the European Journal of Operational Research. This encounter made me realize that Scatter Search has reached a level of maturity as an optimization method that has parallels with what Tabu Search was experiencing in the late eighties. So I thought that the moment was perfect to embark on this project, which has been supported en…
Seawater carbonate chemistry and percentage cover of macroalgal species at three locations at Vulcano, Italy
2017
Beneficial effects of CO2 on photosynthetic organisms will be a key driver of ecosystem change under ocean acidification. Predicting the responses of macroalgal species to ocean acidification is complex, but we demonstrate that the response of assemblages to elevated CO2 are correlated with inorganic carbon physiology. We assessed abundance patterns and a proxy for CO2:HCO3- use (delta 13C values) of macroalgae along a gradient of CO2 at a volcanic seep, and examined how shifts in species abundance at other Mediterranean seeps are related to macroalgal inorganic carbon physiology. Five macroalgal species capable of using both HCO3- and CO2 had greater CO2 use as concentrations increased. Th…
Multicentric, multifocal, and recurrent osteoid osteoma of the hip: first case report.
2019
Abstract Background Osteoid osteoma is a benign bone-forming tumour, which very unfrequently has multifocal or multicentric presentation. We report the first known case of a multicentric, multifocal and recurrent osteoid osteoma treated using radiofrequency ablation. Case presentation A 39-year-old man with two-year history of left hip pain was admitted at our Institution. The pain was more intense during the night and partially relieved by salicylates. Pelvis CT demonstrated two lytic lesions (8 and 7 mm, respectively) with surrounding sclerotic reactive bone, both with a central focal area of high attenuation, located in the femoral neck and along the anterior portion of the acetabulum, r…