Doutorado em Ciência da Computação
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Navegando Doutorado em Ciência da Computação por Por Orientador "Barbosa, Rommel Melgaço"
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Item Uso e estabilidade de seletores de variáveis baseados nos pesos de conexão de redes neurais artificiais(Universidade Federal de Goiás, 2021-03-19) Costa, Nattane Luíza da; Barbosa, Rommel Melgaço; http://lattes.cnpq.br/6228227125338610; Barbosa, Rommel Melgaço; Lima, Márcio Dias de; Lins, Isis Didier; Costa, Ronaldo Martins da; Leitão Júnior, Plínio de SáArtificial Neural Networks (ANN) are machine learning models used to solve problems in several research fields. Although, ANNs are often considered “black boxes”, which means that these models cannot be interpreted, as they do not provide explanatory information. Connection Weight Based Feature Selectors (WBFS) have been proposed to extract knowledge from ANNs. Most of studies that have been using these algorithms are based on just one ANN model. However, there are variations in the ANN connection weight values due to the initialization and training, and consequently, leading to variations in the importance ranking generated by a WBFS. In this context, this thesis presents a study about the WBFS. First, a new voting approach is proposed to assess the stability of the WBFS, i.e, the variation in the result of the WBFS. Then, we evaluated the stability of the algorithms based on multilayer perceptron (MLP) and extreme learning machines (ELM). Furthermore, an improvement is proposed in the algorithms of Garson, Olden, and Yoon, combining them with the feature selector ReliefF. The new algorithms are called FSGR, FSOR, and FSYR. The experiments were performed based on 28 MLP architectures, 16 ELM architectures, and 16 data sets from the UCI Machine Learning Repository. The results show that there is a significant difference in WBFS stability depending on the training parameters of the ANNs and depending on the WBFS used. In addition, the proposed algorithms proved to be more effective than the classic algorithms. As far as we know, this study was the first attempt to measure the stability of WBFS, to investigate the effects of different ANN training parameters on the stability of WBFS, and the first to propose a combination of WBFS with another feature selector. Besides, the results provide information about the benefits and limitations of WBFS and represent a starting point for improving the stability of these algorithms.Item Abordagem de seleção de características baseada em AUC com estimativa de probabilidade combinada a técnica de suavização de La Place(Universidade Federal de Goiás, 2024-09-28) Ribeiro, Guilherme Alberto Sousa; Costa, Nattane Luíza da; http://lattes.cnpq.br/9968129748669015; Barbosa, Rommel Melgaço; http://lattes.cnpq.br/6228227125338610; Barbosa, Rommel Melgaço; Lima, Marcio Dias de; Oliveira, Alexandre César Muniz de; Gonçalves, Christiane; Rodrigues, Diego de CastroThe high dimensionality of many datasets has led to the need for dimensionality reduction algorithms that increase performance, reduce computational effort and simplify data processing in applications focused on machine learning or pattern recognition. Due to the need and importance of reduced data, this paper proposes an investigation of feature selection methods, focusing on methods that use AUC (Area Under the ROC curve). Trends in the use of feature selection methods in general and for methods using AUC as an estimator, applied to microarray data, were evaluated. A new feature selection algorithm, the AUC-based feature selection method with probability estimation and the La PLace smoothing method (AUC-EPS), was then developed. The proposed method calculates the AUC considering all possible values of each feature associated with estimation probability and the La Place smoothing method. Experiments were conducted to compare the proposed technique with the FAST (Feature Assessment by Sliding Thresholds) and ARCO (AUC and Rank Correlation coefficient Optimization) algorithms. Eight datasets related to gene expression in microarrays were used, all of which were used for the crossvalidation experiment and four for the bootstrap experiment. The results showed that the proposed method helped improve the performance of some classifiers and in most cases with a completely different set of features than the other techniques, with some of these features identified by AUC-EPS being critical for disease identification. The work concluded that the proposed method, called AUC-EPS, selects features different from the algorithms FAST and ARCO that help to improve the performance of some classifiers and identify features that are crucial for discriminating cancer.Item Abordagem de seleção de características baseada em AUC com estimativa de probabilidade combinada a técnica de suavização de La Place(Universidade Federal de Goiás, 2023-09-28) Ribeiro, Guilherme Alberto Sousa; Costa, Nattane Luíza da; http://lattes.cnpq.br/9968129748669015; Barbosa, Rommel Melgaço; http://lattes.cnpq.br/6228227125338610; Barbosa, Rommel Melgaço; Lima, Marcio Dias de; Oliveira, Alexandre César Muniz de; Gonçalves, Christiane; Rodrigues, Diego de CastroThe high dimensionality of many datasets has led to the need for dimensionality reduction algorithms that increase performance, reduce computational effort and simplify data processing in applications focused on machine learning or pattern recognition. Due to the need and importance of reduced data, this paper proposes an investigation of feature selection methods, focusing on methods that use AUC (Area Under the ROC curve). Trends in the use of feature selection methods in general and for methods using AUC as an estimator, applied to microarray data, were evaluated. A new feature selection algorithm, the AUC-based feature selection method with probability estimation and the La PLace smoothing method (AUC-EPS), was then developed. The proposed method calculates the AUC considering all possible values of each feature associated with estimation probability and the LaPlace smoothing method. Experiments were conducted to compare the proposed technique with the FAST (Feature Assessment by Sliding Thresholds) and ARCO (AUC and Rank Correlation coefficient Optimization) algorithms. Eight datasets related to gene expression in microarrays were used, all of which were used for the cross-validation experiment and four for the bootstrap experiment. The results showed that the proposed method helped improve the performance of some classifiers and in most cases with a completely different set of features than the other techniques, with some of these features identified by AUC-EPS being critical for disease identification. The work concluded that the proposed method, called AUC-EPS, selects features different from the algorithms FAST and ARCO that help to improve the performance of some classifiers and identify features that are crucial for discriminating cancer.Item Aprimoramento do modelo de seleção dos padrões associativos: uma abordagem de mineração de dados(Universidade Federal de Goiás, 2021-12-20) Rodrigues, Diego de Castro; Barbosa, Rommel Melgaço; http://lattes.cnpq.br/6228227125338610; Barbosa, Rommel Melgaço; Costa, Ronaldo Martins da; Costa, Nattane Luíza da; Rocha, Marcelo Lisboa; Jorge, Lúcio de CastroThe objective of this study is to improve the association rule selection model through a set of asymmetric probabilistic metrics. We present the Health Association Rules - HAR, based on Apriori, the algorithm is composed of six functions and uses alternative metrics to the Support/Confidence model to identify the implication X → Y . Initially, the application of our solution was focused only on health data, but we realized that asymmetrical associative patterns could be applied in other contexts that seek to address the cause and effect of a pattern. Our experiments were composed of 60 real datasets taken from specialist websites, research partnerships and open data. We empirically observed the behavior of HAR in all data sets, and a comparison was performed with the classical Apriori algorithm. We realized that it has overcome the main problems of the Support/Confidence model. We were able to identify the most relevant patterns for the observed datasets, eliminating logical contradictions and redundancies. We also perform a statistical analysis of the experiments where the statistical effect is positive for HAR. HAR was able to discover more representative patterns and rare patterns, in addition to being able to perform rule grouping, filtering and ranking. Our solution presented a linear behavior in the experiments, being able to be applied in health, social, content suggestion, product indication and educational data. Not limited to these data domains, HAR is prepared to receive large amounts of data by using a customized parallel architecture.Item Sobre alianças defensivas e ofensivas globais em alguns produtos de grafos e grafos simpliciais(Universidade Federal de Goiás, 2015-10-30) Silva, Leila Roling Scariot da; Dourado, Mitre Costa; http://lattes.cnpq.br/0841425239502177; Barbosa, Rommel Melgaço; http://lattes.cnpq.br/6228227125338610; Barbosa, Rommel Melgaço; Dourado, Mitre Costa; Federson, Fernando Marques; Rosa, Thierson Couto; Santos, José Plínio de OliveiraGiven a graph G, a defensive alliance of a set of vertices A⊆V(G) satisfying the condition that for each v ∈ A, |N[v] ∩ A| ≤ |N[v] − A|. The set S is an offensive alliance if the inaquality holds for every v ∈ N[S]−S. A alliance A is called global if is also a dominant set. In this paper, we establish lower bounds for Simplicial Graphs and further give closed formulas and upper bounds to decide the global, defensive, offensive, alliance numbers for lexicographic product of paths, cycles, stars and complete graphs. We establish a relationship to global defensive alliance numbers and complementary prism product to graphs.