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Play-Persona: Modeling Player Behaviour in Computer Games

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7.2 ESOM<br />

Fig. 4. Rectangular lattice map organized <strong>in</strong> a toroid shape; SOM size: 50 X 100 neurons.<br />

As previously mentioned <strong>in</strong> Section 5, a toroid-shaped ESOM structured <strong>in</strong> a sheet grid is utilized to<br />

identify classes of play<strong>in</strong>g behavior <strong>in</strong> TRU. Fig. 4 depicts the 50 100 neuron structure used <strong>in</strong> the<br />

experiments presented <strong>in</strong> this paper. The number of 5000 neurons is chosen to provide a good<br />

compromise between tra<strong>in</strong><strong>in</strong>g performance, computational effort and resolution detail of the map.<br />

The toroid shape of the map is selected due to border effects observed <strong>in</strong> tra<strong>in</strong><strong>in</strong>g attempts with 2-<br />

dimensional sheet maps.<br />

1) ESOM tra<strong>in</strong><strong>in</strong>g: The weight vector of the ESOM is randomly <strong>in</strong>itialized us<strong>in</strong>g a<br />

Gaussian distribution; the mean and standard deviation of the distribution are set to the respective<br />

values of the correspond<strong>in</strong>g <strong>in</strong>put feature. The <strong>in</strong>itial neighborhood size is set to 25 which l<strong>in</strong>early<br />

drops to 1 while the weight<strong>in</strong>g neighbor function, h, used is the Gaussian kernel. The learn<strong>in</strong>g rate<br />

is set to 0.7 but is decreased l<strong>in</strong>early dur<strong>in</strong>g tra<strong>in</strong><strong>in</strong>g reach<strong>in</strong>g the value of 0.1 at the end of the 100<br />

tra<strong>in</strong><strong>in</strong>g epochs used. The tra<strong>in</strong><strong>in</strong>g samples are presented <strong>in</strong> a randomly permuted order at each<br />

epoch of the algorithm. In order to m<strong>in</strong>imize the effect of non-determ<strong>in</strong>istic selection of <strong>in</strong>itial<br />

218

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