1 | package de.ugoe.cs.eventbench.models;
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2 |
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3 | import java.security.InvalidParameterException;
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4 | import java.util.Collection;
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5 | import java.util.LinkedList;
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6 | import java.util.List;
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7 | import java.util.Random;
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8 |
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9 | import de.ugoe.cs.eventbench.data.Event;
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10 |
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11 | /**
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12 | * <p>
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13 | * Implements a Deterministic Finite Automata (DFA) capable of random session
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14 | * generation. It is a special case of a first-order Markov model, where the
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15 | * transition probability is equally high for all following states.
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16 | * </p>
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17 | *
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18 | * @author Steffen Herbold
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19 | * @version 1.0
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20 | */
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21 | public class DeterministicFiniteAutomaton extends FirstOrderMarkovModel {
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22 |
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23 | /**
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24 | * <p>
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25 | * Id for object serialization.
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26 | * </p>
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27 | */
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28 | private static final long serialVersionUID = 1L;
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29 |
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30 | /**
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31 | * <p>
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32 | * Constructor. Creates a new DeterministicFiniteAutomaton.
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33 | * </p>
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34 | *
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35 | * @param r
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36 | * random number generator used by probabilistic methods of the
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37 | * class
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38 | */
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39 | public DeterministicFiniteAutomaton(Random r) {
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40 | super(r);
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41 | }
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42 |
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43 | /**
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44 | * <p>
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45 | * Calculates the proability of the next state. Each of the following states
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46 | * in the automaton is equally probable.
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47 | * </p>
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48 | *
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49 | * @see de.ugoe.cs.eventbench.models.IStochasticProcess#getProbability(java.util.List,
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50 | * de.ugoe.cs.eventbench.data.Event)
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51 | */
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52 | @Override
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53 | public double getProbability(List<? extends Event<?>> context,
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54 | Event<?> symbol) {
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55 | if( context==null ) {
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56 | throw new InvalidParameterException("context must not be null");
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57 | }
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58 | if( symbol==null ) {
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59 | throw new InvalidParameterException("symbol must not be null");
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60 | }
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61 | double result = 0.0d;
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62 |
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63 | List<Event<?>> contextCopy;
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64 | if (context.size() >= trieOrder) {
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65 | contextCopy = new LinkedList<Event<?>>(context.subList(
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66 | context.size() - trieOrder + 1, context.size()));
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67 | } else {
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68 | contextCopy = new LinkedList<Event<?>>(context);
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69 | }
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70 |
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71 | Collection<Event<?>> followers = trie.getFollowingSymbols(contextCopy);
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72 |
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73 | if (followers.size() != 0 && followers.contains(symbol)) {
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74 | result = 1.0d / followers.size();
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75 | }
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76 |
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77 | return result;
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78 | }
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79 |
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80 | }
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