Lucas de Oliveira

Global optimization using a genetic algorithm with hierarchically structured population

This paper applies a genetic algorithm with hierarchically structured population to solve unconstrained optimization problems. The population has individuals distributed in several overlapping clusters, each one with a leader and a variable number of support individuals. The hierarchy establishes that leaders must be fitter than its supporters with the topological organization of the clusters following a tree. Computational tests evaluate different population structures, population sizes and crossover operators for better algorithm performance. A set of known benchmark test problems is solved and the results found are compared with those obtained from other methods described in the literature, namely, two genetic algorithms, a simulated annealing, a differential evolution and a particle swarm optimization. The results indicate that the method employed is capable of achieving better performance than the previous approaches in regard as the two criteria usually employed for comparisons: the number of function evaluations and rate of success. The method also has a superior performance if the number of problems solved is taken into account.

A genetic algorithm/mathematical programming approach to solve a two-level soft drink production problem

This study applies a genetic algorithm embedded with mathematical programming techniques to solve a synchronized and integrated two-level lot sizing and scheduling problem motivated by a real-world problem that arises in soft drink production. The problem considers a production process compounded by raw material preparation/storage and soft drink bottling. The lot sizing and scheduling decisions should be made simultaneously for raw material preparation/storage in tanks and soft drink bottling in several production lines minimizing inventory, shortage and setup costs. The literature provides mixed-integer programming models for this problem, as well as solution methods based on evolutionary algorithms and relax-and-fix approaches. The method applied by this paper uses a new approach which combines a genetic algorithm (GA) with mathematical programming techniques. The GA deals with sequencing decisions for production lots, so that an exact method can solve a simplified linear programming model, responsible for lot sizing decisions. The computational results show that this evolutionary/mathematical programming approach outperforms the literature methods in terms of production costs and run times when applied to a set of real-world problem instances provided by a soft drink company.

Improved bounds for the traveling umpire problem: A stronger formulation and a relax-and-fix heuristic

Given a double round-robin tournament, the traveling umpire problem (TUP) consists of determining which games will be handled by each one of several umpire crews during the tournament. The objective is to minimize the total distance traveled by the umpires, while respecting constraints that include visiting every team at home, and not seeing a team or venue too often. We strengthen a known integer programming formulation for the TUP and use it to implement a relax-and-fix heuristic that improves the quality of 24 out of 25 best-known feasible solutions to instances in the TUP benchmark. We also improve all best-known lower bounds for those instances and, for the first time, provide lower bounds for instances with more than 16 teams.

On the complexity of the traveling umpire problem

The traveling umpire problem (TUP) consists of determining which games will be handled by each one of several umpire crews during a double round-robin tournament. The objective is to minimize the total distance traveled by the umpires, while respecting constraints that include visiting every team at home, and not seeing a team or venue too often. Even small instances of the TUP are very difficult to solve, and several exact and heuristic approaches for it have been proposed in the literature. To this date, however, no formal proof of the TUPs computational complexity exists. We prove that the decision version of the TUP is NP -complete for certain values of its input parameters.

Lower bounds for large traveling umpire instances

Given a double round-robin tournament, the Traveling Umpire Problem (TUP) seeks to assign umpires to the games of the tournament while minimizing the total distance traveled by the umpires. The assignment must satisfy constraints that prevent umpires from seeing teams and venues too often, while making sure all games have umpires in every round, and all umpires visit all venues. We propose a new integer programming model for the TUP that generalizes the two best existing models, introduce new families of strong valid inequalities, and implement a branch-and-cut algorithm to solve instances from the TUP benchmark. When compared against published state-of-the-art methods, our algorithm significantly improves all best known lower bounds for large TUP instances (with 20 or more teams). HighlightsAn integer programming model that generalizes the two best models in the literature.New families of strong valid inequalities for the generalized model.Significantly better lower bounds for all benchmark instances with 20 or more teams.

Preoperative evaluation for the use of cranial halo traction in the spine treatment of rigid deformities

OBJETIVO: evaluar, retrospectivamente, la eficacia y la seguridad del uso del halo craneal gravitacional como tecnica de tratamiento de deformidades rigidas de la columna vertebral, y rever complicaciones asociadas a su tratamiento. METODOS: ha sido analizado un total de diez pacientes con deformidades rigidas de la columna vertebral: cifosis, escoliosis, cifoscoliosis e hiperlordosis cervical. El criterio para inclusion de los pacientes fue el uso del halo craneal gravitacional en un periodo preoperatorio y interoperatorio en deformidades rigidas de la columna vertebral. Han sido evaluados los prontuarios de los pacientes y sus mediciones radiograficas en un periodo preoperatorio, tras la instalacion del halo craneal gravitacional y en el periodo postoperatorio. Las variables estudiadas fueron: edad, sexo, valor angular de la curva principal, valor angular de la curva secundaria, valor angular de la curva sagital mayor, protocolo de traccion y tipo de procedimiento utilizado. RESULTADOS: en relacion al plano frontal, se ha evaluado, en el periodo preoperatorio, la media angular de 89,9o, decreciendo para 65,0o tras la instalacion del halo y 56,9o en el postoperatorio. Analizando el plano sagital, se observa en el periodo preoperatorio el valor angular de 77,7o, decreciendo para 55,4o con el uso del halo y 46,5o en el postoperatorio. CONCLUSION: se puede concluir que el uso de la traccion de halo craneal es un metodo eficaz para ayudar a corregir las deformidades de la columna rigida, ya que se logro una significativa correccion de las deformidades antes de la operacion por los periodos despues de la instalacion de halo y postoperatorio, sin previo aviso u otras complicaciones neurologicas graves.

Avaliação pré-operatória visando ao uso do halo craniano no tratamento de deformidades rígidas da coluna vertebral

OBJETIVO: evaluar, retrospectivamente, la eficacia y la seguridad del uso del halo craneal gravitacional como tecnica de tratamiento de deformidades rigidas de la columna vertebral, y rever complicaciones asociadas a su tratamiento. METODOS: ha sido analizado un total de diez pacientes con deformidades rigidas de la columna vertebral: cifosis, escoliosis, cifoscoliosis e hiperlordosis cervical. El criterio para inclusion de los pacientes fue el uso del halo craneal gravitacional en un periodo preoperatorio y interoperatorio en deformidades rigidas de la columna vertebral. Han sido evaluados los prontuarios de los pacientes y sus mediciones radiograficas en un periodo preoperatorio, tras la instalacion del halo craneal gravitacional y en el periodo postoperatorio. Las variables estudiadas fueron: edad, sexo, valor angular de la curva principal, valor angular de la curva secundaria, valor angular de la curva sagital mayor, protocolo de traccion y tipo de procedimiento utilizado. RESULTADOS: en relacion al plano frontal, se ha evaluado, en el periodo preoperatorio, la media angular de 89,9o, decreciendo para 65,0o tras la instalacion del halo y 56,9o en el postoperatorio. Analizando el plano sagital, se observa en el periodo preoperatorio el valor angular de 77,7o, decreciendo para 55,4o con el uso del halo y 46,5o en el postoperatorio. CONCLUSION: se puede concluir que el uso de la traccion de halo craneal es un metodo eficaz para ayudar a corregir las deformidades de la columna rigida, ya que se logro una significativa correccion de las deformidades antes de la operacion por los periodos despues de la instalacion de halo y postoperatorio, sin previo aviso u otras complicaciones neurologicas graves.

Evaluación pre-operatoria del uso del halo craneal en lo tratamiento de las deformidades rígidas de la columna vertebral

OBJETIVO: evaluar, retrospectivamente, la eficacia y la seguridad del uso del halo craneal gravitacional como tecnica de tratamiento de deformidades rigidas de la columna vertebral, y rever complicaciones asociadas a su tratamiento. METODOS: ha sido analizado un total de diez pacientes con deformidades rigidas de la columna vertebral: cifosis, escoliosis, cifoscoliosis e hiperlordosis cervical. El criterio para inclusion de los pacientes fue el uso del halo craneal gravitacional en un periodo preoperatorio y interoperatorio en deformidades rigidas de la columna vertebral. Han sido evaluados los prontuarios de los pacientes y sus mediciones radiograficas en un periodo preoperatorio, tras la instalacion del halo craneal gravitacional y en el periodo postoperatorio. Las variables estudiadas fueron: edad, sexo, valor angular de la curva principal, valor angular de la curva secundaria, valor angular de la curva sagital mayor, protocolo de traccion y tipo de procedimiento utilizado. RESULTADOS: en relacion al plano frontal, se ha evaluado, en el periodo preoperatorio, la media angular de 89,9o, decreciendo para 65,0o tras la instalacion del halo y 56,9o en el postoperatorio. Analizando el plano sagital, se observa en el periodo preoperatorio el valor angular de 77,7o, decreciendo para 55,4o con el uso del halo y 46,5o en el postoperatorio. CONCLUSION: se puede concluir que el uso de la traccion de halo craneal es un metodo eficaz para ayudar a corregir las deformidades de la columna rigida, ya que se logro una significativa correccion de las deformidades antes de la operacion por los periodos despues de la instalacion de halo y postoperatorio, sin previo aviso u otras complicaciones neurologicas graves.