A new chromosome encoding method, named fuzzy coding, is proposed for representing real number parameters in a genetic algorithm. Fuzzy coding provides the value of a parameter on the basis of the optimum number of selected fuzzy sets and...
moreA new chromosome encoding method, named fuzzy coding, is proposed for representing real number parameters in a genetic algorithm. Fuzzy coding provides the value of a parameter on the basis of the optimum number of selected fuzzy sets and their effectiveness in terms of degree of membership. Thus, it represents the knowledge associated with each parameter and is an indirect method of encoding compared with alternatives, where the parameters are directly represented in the encoding. Fuzzy coding is described and compared with conventional binary coding, gray coding, and floating-point coding. Two test examples, along with neural identification of a nonlinear pH process from experimental data, are studied. It is shown that fuzzy coding is better than the conventional methods and is effective for parameter optimization in problems where the search space is complicated. Index Terms-Binary coding, floating-point coding, fuzzy coding, genetic algorithm, gray coding, neural networks, nonlinear identification. NOMENCLATURE GA Genetic algorithm. EC Evolutionary computation. LM Local model. RBF Radial basis function. MLP Multilayer perceptron. MSE Mean-square error. Grad Gradient learning method. Binary coding. Gray coding. Real number coding. NM Negative medium. NS Negative small. ZR Zero. PS Positive small. PM Positive medium. Degree of membership function. Lower range of a parameter. Upper range of a parameter. Width of membership functions. Crossover probability. Mutation probability. Value of a parameter from linear membership functions. FS Fuzzy sigmoid distribution. FG Fuzzy Gaussian distribution. FN Fuzzy normal distribution.