Browsing by Author "Grilo, Carlos Fernando Almeida"
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- An automatic generation of textual pattern rules for digital content filters proposal, using grammatical evolution genetic programmingPublication . Basto-Fernandes, Vitor; Yevseyeva, Iryna; Frantz, Rafael Z.; Grilo, Carlos Fernando Almeida; Díaz, Noemí Pérez; Emmerich, Michael
- Aplicação de algoritmos evolucionários à extracção de padrões musicaisPublication . Grilo, Carlos Fernando AlmeidaA extracção de padrões é um problema que se coloca em várias áreas como, por exemplo, a biologia molecular ou a área financeira, e que pode ser considerado, do ponto de vista da inteligência artificial, como uma forma de aprendizagem não supervisionada. No domínio musical, o problema pode ser definido, informalmente, da seguinte forma: dada uma peça musical (ou várias), identificar as partes dessa peça que se repitam, aproximadamente ou não, e que possuam um significado relevante no contexto dessa peça. O objectivo deste trabalho consistiu em estudar a viabilidade da aplicação de algoritmos evolucionários ao problema da extracção de padrões musicais. Para levar a cabo o estudo proposto desenvolvemos duas abordagens utilizando dois tipos diferentes de algoritmos evolucionários: a programação genética e os algoritmos genéticos. Em cada uma das abordagens o objectivo é essencialmente o mesmo: encontrar uma segmentação de uma peça que permita identificar os padrões mais importantes nela existentes. Devido às características de cada um dos algoritmos, a representação utilizada para os indivíduos é diferente. Assim, enquanto que na abordagem baseada em programação genética cada indivíduo é um programa que produz como resultado uma determinada peça, constituindo ao mesmo tempo uma descrição da sua estrutura de segmentos, na abordagem baseada em algoritmos genéticos cada indivíduo consiste numa sequência de símbolos que representa uma hipótese de segmentação da peça a analisar. Embora as funções de avaliação utilizadas nas duas abordagens também sejam diferentes, ambas beneficiam os indivíduos que apresentem o conjunto dos padrões mais importantes existentes na peça. Para ambas as abordagens foi também desenvolvido um método que permite realizar uma segunda segmentação de uma peça a partir dos segmentos identificados na primeira segmentação. Os resultados experimentais obtidos com a abordagem baseada em programação genética que desenvolvemos permitem-nos verificar que esta abordagem apresenta bastantes dificuldades na resolução deste tipo de problemas. Pelo contrário, a abordagem baseada em algoritmos genéticos permitiu obter resultados que nos levam a considerar que a aplicação desta abordagem a este tipo de problemas é viável.
- Asynchronous stochastic dynamics and the spatial prisioner's dilemma gamePublication . Grilo, Carlos Fernando Almeida; Correia, LuísWe argue that intermediate levels of asynchronism should be explored when one uses evolutionary games to model biological and sociological systems. Usually, only perfect synchronism and continuous asynchronism are used, assuming that it is enough to test the model under these two opposite update methods. We believe that biological and social systems lie somewhere between these two extremes and that we should inquire how the models used in these situations behave when the update method allows more than one element to be active at the same time but not necessarily all of them. Here, we use an update method called Asynchronous Stochastic Dynamics which allows us to explore intermediate levels of asynchronism and we apply it to the Spatial Prisoner’s Dilemma game. We report some results concerning the way the system changes its behaviour as the synchrony rate of the update method varies.
- Composing music with case-based reasoningPublication . Pereira, Francisco C.; Grilo, Carlos Fernando Almeida; Macedo, Luís; Cardoso, Fernando Amílcar BandeiraMusic is one of the most intriguing and joyful domain of research and analysis. Driven by this insatiable curiosity, Musical Analysis has emerged to formally understand and structure music and its intrinsic intention and causality. Each complete analysis of a piece points to issues that go far beyond the normal graphical music representation. A better analysis is important not only to a better interpretation, but also to a more perfect composition. An exceptional composer is indeed an exceptional analyst. This paper presents a computational approach to music composition through the use and exploration of musical analysis. Centered on Case-Based Reasoning and Planning techniques, it consists on creating new solutions by keeping, transforming and extrapolating knowledge from already expert-made music analysis. For our approach, each analysis is represented as a precisely structured Case, divisible into all of its components. The process of composition we adopt is progressive, left-to-right, and top-to-bottom and has some similarities with (Wallas’ 1926) theory for creative production (Macedo et al. 1996a) which we adapted for this specifically structured and complex domain. The resulting implemented program has already generated several different musical pieces, which were examined and analyzed by experts, bringing up precious questions and advice.
- Effects of asynchronism on evolutionary gamesPublication . Grilo, Carlos Fernando Almeida; Correia, LuísWe analyze the influence of the update dynamics on symmetric 2-player evolutionary games, which are among the most used tools to study the emergence of cooperation in populations of interacting agents. A synchronous dynamics means that, at each time step, all the agents of the population update their strategies simultaneously. An extreme case of asynchronism is sequential dynamics, in which only one agent is updated each time. We first show that these two opposite update dynamics can lead to very different outcomes and that sequential dynamics is detrimental to the emergence of cooperation only when the probability of imitating the most successful neighbors is high. In this sense, we can say that, when the update dynamics has some influence, in general asynchronism is beneficial to the emergence of cooperation.Wethen explore the consequences of using intermediate levels of asynchronism, where only a fraction of the agents update their behavior each time. In general, the level of cooperation changes smoothly and monotonically as we gradually go from synchronous to sequential dynamics. However, there are some exceptions that should be taken into account. In addition, the results show that the possibility of agents taking irrational decisions has a key role in the sensitivity of thesemodels to changes in the update dynamics. Explanations for the observed behaviors are advanced.
- Experimental study of a similarity metric for retrieving pieces from structured plan cases: its role in the originality of plan case solutionsPublication . Macedo, Luís; Pereira, Francisco C.; Grilo, Carlos Fernando Almeida; Cardoso, Fernando Amílcar BandeiraThis paper describes a quantitative similarity metric and its contribution to achieve original plan solutions. This similarity metric is used by an iterative process of piece retrieval from structured plan cases. Within our approach plan cases are tree-like networks of pieces (goals and actions). These case pieces are ill-related each other by links (explanations). These links may be classified as hierarchical or temporal, antecedent or consequent, and explicit or implicit. Besides links, each case piece has also information about its properties (the attributes-value pairs), its hierarchical and temporal position in the case (the address), and about its constraints in the relationship with others (the constraints). The similarity metric computes a similarity value between two case pieces taking into account similarities between these case piece’s information types. Each time a problem is proposed, different weights are given to some of those similarities, with the aim of solving it with an original solution. This similarity metric is used by the system INSPIRER (ImagiNation taking as Source Past and Imperfectly REalated Reasonings). We illustrate the role of the similarity metric in the creativity of solutions, focusing specially their originality, with the presentation of the experimental results obtained in the musical composition domain, which is considered by us as a planning domain.
- How to build the network of contacts : selecting the cooperative partnersPublication . Mariano, Pedro; Correia, Luís; Grilo, Carlos Fernando AlmeidaWe address the problem of finding the correct agents to interact with from a general standpoint. We take the payout obtained by agents in any game with dilemma as an input to our model. Its output is a probability distribution used in the partner selection that increasingly favours cooperative agents. Our approach contrasts with others designed for specific games without concerns of generality. We show both theoretically and experimentally that the major factor affecting cooperators selecting only themselves is the agents' strategies. This result does not depend on game nature or the initial probability distribution.
- Influência da dinâmica de actualização na evolução da cooperaçãoPublication . Grilo, Carlos Fernando Almeida; Correia, Luís Miguel Parreira eA identificação dos mecanismos que permitem promover a emergência e a manutenção de comportamentos de cooperação é um problema com relevância em diversas disciplinas científicas tais como a Biologia, a Sociologia, a Economia e a Informática. Numa população de indivíduos que interagem entre si, estes decidem, de vez em quando, alterar a forma como agem nas interacções em que participam. Potencialmente, a relação temporal entre os processos de actualização que ocorrem na população pode influenciar a proliferação de comportamentos cooperativos uma vez que condiciona a informação disponível da qual estes processos dependem. Esta relação estabelece uma dinâmica que denominamos por dinâmica de actualização. A actualização diz-se síncrona se os agentes actualizam a sua estratégia em simultâneo e assíncrona em caso contrário. Neste trabalho investigamos a influência da dinâmica de actualização na evolução da cooperação utilizando como plataforma de trabalho a Teoria dos Jogos Evolucionária. Os resultados mostram que, em geral, quando a dinâmica de actualização tem alguma influência, o assincronismo é benéfico à evolução da cooperação, ou seja, que é um mecanismo de promoção de comportamentos de cooperação numa população de indivíduos. O resultados são suportados pela utilização de uma grande variedade de condições, a qual permite proceder a uma caracterização da forma como a influência da dinâmica de actualização varia com as condições do sistema e a uma identificação dos aspectos que desempenham um papel relevante nessa influência.
- Instability in spatial evolutionary gamesPublication . Grilo, Carlos Fernando Almeida; Correia, LuísWe investigate the aspects that influence the instability of spatial evolutionary games, namely the Prisoner's Dilemma and the Snowdrift games. In this paper instability is defined as the proportion of strategy changes in the asymptotic period of the evolutionary process. The results show that with the Prisoner's Dilemma, when the level of noise present in the decision process is very low, the instability decreases as the synchrony rate decreases. With the Snowdrift this pattern of behavior depends strongly on the interaction topology and arises only for random and scale-free networks. However, for large noise values, the instability in both games depends only on the proportion of cooperators present in the population: it increases as the proportion of cooperators approaches 0.5. We advance an explanation for this behavior.
- Musical pattern extraction using genetic algorithmsPublication . Grilo, Carlos Fernando Almeida; Cardoso, Fernando Amílcar BandeiraThis paper describes a research work in which we study the possibility of applying genetic algorithms to the extraction of musical patterns in monophonic musical pieces. Each individual in the population represents a possible segmentation of the piece being analysed. The goal is to find a segmentation that allows the identification of the most significant patterns of the piece. In order to calculate an individual’s fitness, all its segments are compared among each other. The bigger the area occupied by similar segments the better the quality of the segmentation.