Dinâmicas emergentes na família de memórias associativas bidirecionais caóticas e sua habilidade para saltar passos / Emergent dynamics in family of chaotic bidirectional associative memories and its ability to skip steps

AUTOR(ES)
DATA DE PUBLICAÇÃO

2006

RESUMO

In this thesis, a family of bidirectional associative memories (C-BAM family) is proposed, implemented and tested to extend the study of chaotic phenomenon in associative models. In the C-BAM model, all the original neurons of bidirectional associative memory (BAM), BAM with delay and exponenetial BAM (eBAM) were substituted for chaotic neurons. Based on the experimental design, values of C-BAM family parameters are set to illustrate the emergence of a diversity of dynamic behavior, such as bifurcation, deterministic chaos and crisis. The existence of the chaotic dynamics is confirmed by calculation of Lyapunov exponents. Empiric experiments showed that the chaotic dynamics modifies the behavior of memory accessibility. Instead of recalling a single pair, as BAM did, its chaotic version yielded a wide diversity of recalled patterns, involving complex transitions via memorized patterns for some parametric variations. Hence, C-BAM family can access patterns that original BAM family cannot. Moreover, the new way of memory accessibility, in which several recall sequences (with distinct sizes) composed of trained and nontrained patterns have emerged, can be used to model the ability of skipping steps by an individual in a task solution. This thesis selected C-BAM network to illustrate that the retrieval sequence can model the ability of a novice or the ability of an expert to execute a task. There are also illustrated cases in which a novice recall can be transformed into an expert recall through parametric variation. Although C-BAM family can reach all stored patterns during the chaotic behavior, it can not converge towards a specific pattern, consequently a desired output is not produced. In this thesis, two control strategies are proposed in order to make the chaotic networks to converge towards the desired memory: the pinning control method and the adaptive control method. Consequently, the C-BAM models can effectively realize the correct heteroassociation to former non-accessible memories and the C-BAM network can quickly be stabilized in the final state of a task, given the first state

ASSUNTO(S)

fenômeno saltar passos bidirectional associative memories chaos control retrieval of memories recuperação de memórias step skipping phenomenon controle de caos chaotic dynamics memórias associativas bidirecionais dinâmicas caóticas

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