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The Development of Neural Network Based System Identification ...

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4.2 THE ARTIFICIAL NEURAL NETWORKS 79<br />

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<br />

<br />

<br />

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<br />

(a) Linear Classifier<br />

(b) Linear classifier or<br />

predictor<br />

(c) Non-linear classifier<br />

or predictor<br />

(d) Unsupervised classifier (e) Unsupervised clustering/spatial<br />

relationship<br />

<br />

<br />

<br />

<br />

<br />

<br />

- Context Units<br />

(f) Time series forecasting<br />

Figure 4.1 Different types <strong>of</strong> NN modelling architectures: (a) Single-layer perceptron; (b) Linear<br />

neuron; (c) Multi-layer perceptron (MLP); (d) Competitive network; (e) Self-organising feature map<br />

(SOFM); and (f) Recurrent networks<br />

2006]. In this chapter, the MLP, Elman network and their respective variants are used<br />

for the system identification application.<br />

All <strong>of</strong> these networks presented in Figure 4.1 contain many links connecting inputs<br />

to neurons and from neurons to outputs. <strong>The</strong>se network connections are also popularly<br />

known as weights which are allowed to freely adapt to the training data by the learning<br />

algorithms. <strong>The</strong>se weights are also regarded as free parameters as in regression modelling<br />

in statistics. Thus, this would make the neural networks similar to the parametric<br />

models involving the estimation <strong>of</strong> optimum parameters [Samarasinghe, 2007].

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