Reinforcement Learning for Data Mining Based Evolution Algorithm
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Reinforcement Learning for Data Mining Based Evolution Algorithm for TSK-type Neural Fuzzy Systems Design Sheng-Fuu Lin, Yi-Chang Cheng, Jyun-Wei Chang, and Yung-Chi Hsu Department of Electrical and Control Engineering, National Chiao Tung University Hsinchu, Taiwan, R.O.C. ABSTRACT membership functions of a fuzzy controller, with the fuzzy rule This paper proposed a TSK-type neural fuzzy system set assigned in advance. Juang [5] proposed the CQGAF to (TNFS) with reinforcement learning for data mining based simultaneously design the number of fuzzy rules and free evolution algorithm (R-DMEA). In R-DMEA, the group-based parameters in a fuzzy system. In [6], the group-based symbiotic symbiotic evolution (GSE) is adopted that each group represents evolution (GSE) was proposed to solve the problem that all the the set of single fuzzy rule. The R-DMEA contains both fuzzy rules were encoded into one chromosome in the structure learning and parameter learning. In the structure traditional genetic algorithm. In the GSE, each chromosome learning, the proposed R-DMEA uses the two-step self-adaptive represents a single rule of fuzzy system. The GSE uses algorithm to decide the suitable number of rules in a TNFS. In group-based population to evaluate the fuzzy rule locally. parameter learning, the R-DMEA uses the mining-based Although GSE has a better performance when compared with selection strategy to decide the selected groups in GSE by the tradition symbiotic evolution, the combination of groups is data mining method called frequent pattern growth. Illustrative fixed. example is conducted to show the performance and applicability Although the above evolution learning algorithms [4]-[6] of R-DMEA. can improve the traditional genetic algorithms, these algorithms may encounter one or more of the following problems: 1) all the Keywords : Neural fuzzy system, control, group-based fuzzy rules are encoded into one chromosome; 2) the numbers symbiotic evolution, reinforcement learning, FP-Growth. of fuzzy rules have to be assigned in advance; 3) the population cannot evaluate each fuzzy rule locally. In this paper, a TSK-type neural fuzzy system (TNFS) 1. INTRODUCTION with reinforcement learning for data mining based evolution Recently, a fuzzy system used for control problems has algorithm (R-DMEA) is proposed to solve the aforementioned become a popular research topic. A fuzzy system consists of a problems. The R-DMEA uses a two-step self-adaptive algorithm set of fuzzy if-then rules. Conventionally, the selection of fuzzy (TSSA) to determine the number of fuzzy rules automatically if-then rules often relies on a substantial amount of heuristic and processes the variable combination of chromosomes applied observations. Obviously, it is difficult for human experts to to the GSE. After the TSSA determines the number of fuzzy examine all the input-output data from a complex system to find rules (in this paper, the number of groups for GSE), R-DMEA proper rules. To cope with this difficulty, several supervised uses a data mining-based selection strategy (MSS) to decide the learning approaches that generate if-then rules from numerical groups selected to construct a TNFS. Data mining is a method data have been proposed [1]. of mining information in the database called transactions. One For some real-world applications, precise training data goal of data mining is to find association rules among frequent are usually difficult and to obtain. Therefore, there has been a item sets in transactions. Hang et al. [7] proposed frequent growing interest in reinforcement learning problems [2] and [3]. pattern growth (FP-Growth) to mine frequent patterns without Recently, the evolutionary method used for training the candidate generation. Since data mining successfully find the fuzzy model has become an important field. The evolutionary information within the large item sets, it should be useful to fuzzy model generates a fuzzy system by incorporating solve the problem of how to select groups to construct TNFS evolutionary learning procedure such as genetic algorithms with many different combinations of fuzzy rules. (GAs). Several genetic fuzzy models have been proposed in In the MSS, groups obtained from FP-Growth are [4]-[6]. In [4], Karr applied GAs to the design of the selected by using three different actions: normal, searching, and exploring actions. After executing MSS, the population can This work was supported in part by National Science Council, search better combination of individuals and simultaneously Taiwan, R.O.C., under Contract No. NSC 97-2221-E-009-091. examine whether the mined combination of individuals 3. A DATA MINING BASED EVOLUTION ALGORITHM encounter the local optimal condition. The DMEA consists of structure and parameter learning. The advantages of the R-DMEA are summarized as In the structure learning, the DMEA determines the number of follows: 1) the TSSA is proposed to decide the suitable number fuzzy rules automatically and processes the variable of rules; 2) the R-DMEA uses group-based symbiotic evolution combination of chromosomes. The length of combination of to evaluate the fuzzy rule locally; 3) the MSS is proposed to chromosomes denotes the number of rules sets forming a TNFS. select the suitable groups. The proposed DMEA adopts the GSE [6] for GAs evolution. In This paper is organized as follows. Section 2 introduces the the GSE [6], a population is divided to several groups. Each TNFS. The proposed data mining based evolution algorithm group represents a set of the chromosomes that belong to one (DMEA) is described in Section 3. Section 4 introduces the fuzzy rule. Each group will execute the reproduction and R-DMEA. Section 5 presents the results of simulation. The crossover operations in each generation independently. The conclusions are summarized in the last section. structure of the chromosome in DMEA is shown in Fig. 1(a). In DMEA, for solving the problem that the numbers of fuzzy rules 2. REVIEW A TSK-TYPE NEURO-FUZZY SYSTEM have to be assigned in advance, the two-step self-adaptive In this paper, a TSK-type fuzzy system with an R-DMEA algorithm (TSSA) is proposed. In TSSA, the building blocks is used to solve a nonlinear control problem. It is a five-layer (BBs) [8] determines the suitable length of groups combined network structure. The functions of the nodes in each layer are together and decides the number of selection times of each described as follows: length of combined groups applied to the TNFS. In Fig. 1(b), Layer1 (Input Node ): The node only transmits input values to the TSSA codes the probability vector into the building blocks layer 2. That is (BBs), Mk represents k rules that used to form a TNFS; V is a (1) M k = (1) ui x i Layer2 (Membership Function Node ): For an external input xi, probability vector represents the suitability of a TNFS model the following Gaussian membership function is used: with k rules. In the TSSA, the maximum number of rules ( Mmax ) 2 and the minimum number of rules ( M ) must be predefined to (1) − min ui m ij (2) u(2) =exp − ij σ 2 prevent the number of fuzzy rules from being generated beyond ij a certain bound. where mij and σij are, respectively, the center and the width of In parameter learning, for selecting suitable groups to the Gaussian membership function of the jth term of the ith construct a TNFS, this study proposes the MSS to select k input variable xi. individuals to form a TNFS by FP-Growth [7]. The goal of Layer 3 (Rule Node ): The function of each rule is FP-Growth is to find the frequent patterns without candidate (3)= (2) (3) generation. In MSS, FP-Growth is used to find the frequent uj∏ u ij i group sets from transactions, which means the collection of Layer 4 (Consequent Node ): The input to a node in layer 4 is well-performed chromosomes selected from Mk groups. After combined with the output delivered from layer 3 and inputs of the frequent group sets have been found, the MSS uses three layer 1. actions to select from Mk groups k rules to form a TNFS. The n (4)= (3) + (4) three actions defined in this paper are normal, searching, and uj uw j(0 j∑ wx ij i ) i=1 exploring action. In DMEA, the coding structure of the where the summation is over all the inputs and wij are the chromosomes must be suitable for GSE. Fig. 1(c) describes the corresponding parameters of the consequent part. coding of a fuzzy rule. Layer 5 (Output Node ): Each node in this layer corresponds to one output variable. The node integrates all the actions recommended by layers 3 and 4 and acts as a defuzzifier with Mk M k M k (4) (3) + ∑uj ∑ uw j(0 j ∑ wx ij i ) = = = (5) y= u (5) =j1 = j 1 i 1 Mk M k (3) (3) ∑uj ∑ u j j=1 j = 1 where Mk is the number of fuzzy rule. value with k rules greater than Best _ Fitness minus a M k predefined threshold value named ThreadFitnessvalues . Step 2. Determine the selection times according to the probability vectors of the BBs as follows: Rp = (Selection _ Times (*) V /Total _Velocy ) Figure 1: (a) The structure of the chromosome in DMEA. (b) M k M k for = ⋅⋅⋅ (12) Coding the probability vector into the building blocks (BBs) in MMMk min, min+ 1, , M max TSSA. (c) Coding a rule into a chromosome in DMEA. Rmax Total_ Velocy= ∑ V (13) M k =R Mk min The learning process of the DMEA in each group where Selection_Times represents total selection times in each involves four major operators: the TSSA, MMS, crossover generation; Rp is the selection times of Mk groups that use to strategy, and mutation strategy.