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C. FERREIRA 9th Online World Conference on Soft Computing in Industrial Applications, 2004 Designing Neural Networks Using Gene Expression Programming Special genetic operators   The evolution of such complex entities composed of different domains and different alphabets requires a special set of genetic operators so that each domain remains intact. The operators of the basic gene expression algorithm (Ferreira 2001) are easily transposed to neural-net encoding chromosomes, and all of them can be used as long as the boundaries of each domain are maintained and alphabets are not mixed up. Mutation was extended to all the domains and continues to be the most important genetic operator. IS and RIS transposition were also implemented in GEP-nets and their action is obviously restricted to heads and tails. However, a special insertion operator was created that operates within Dw and Dt, ensuring the efficient circulation of weights and thresholds in the population (see section 3.1). Another special operator, weights and thresholds’ mutation, was also created in order to directly introduce variation in the set of available weights and thresholds (see section 3.3). The extension of recombination and gene transposition to GEP-nets is straightforward as their actions never result in mixed domains or alphabets. However, for them to work efficiently (i.e., allow an efficient learning), we must be careful in determining which weights and/or thresholds go to which region after the splitting of the chromosomes, otherwise the system is incapable of evolving efficiently. In the case of gene recombination and gene transposition, keeping track of a gene’s weights and thresholds is no difficult task, and these operators work very well in GEP-nets. But in one-point and two-point recombination where chromosomes can be split anywhere, it is impossible to keep track of the weights and thresholds. In fact, if applied straightforwardly, these operators would produce such evolutionary monsters that they would be of little use in multigenic chromosomes. Therefore, for multigenic systems, a special intragenic two-point recombination was created so that the recombination is restricted to a particular gene (see section 3.2). Home | Contents | Previous | Next