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.ArrayList;
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5 | import java.util.LinkedHashSet;
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6 | import java.util.LinkedList;
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7 | import java.util.List;
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8 | import java.util.Random;
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9 | import java.util.Set;
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10 |
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11 | import de.ugoe.cs.eventbench.data.Event;
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12 | import de.ugoe.cs.eventbench.models.Trie.Edge;
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13 | import de.ugoe.cs.eventbench.models.Trie.TrieVertex;
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14 | import edu.uci.ics.jung.graph.Tree;
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15 |
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16 | /**
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17 | * <p>
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18 | * Implements a skeleton for stochastic processes that can calculate
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19 | * probabilities based on a trie. The skeleton provides all functionalities of
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20 | * {@link IStochasticProcess} except
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21 | * {@link IStochasticProcess#getProbability(List, Event)}.
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22 | * </p>
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23 | *
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24 | * @author Steffen Herbold
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25 | * @version 1.0
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26 | */
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27 | public abstract class TrieBasedModel implements IStochasticProcess {
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28 |
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29 | /**
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30 | * <p>
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31 | * Id for object serialization.
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32 | * </p>
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33 | */
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34 | private static final long serialVersionUID = 1L;
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35 |
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36 | /**
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37 | * <p>
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38 | * The order of the trie, i.e., the maximum length of subsequences stored in
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39 | * the trie.
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40 | * </p>
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41 | */
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42 | protected int trieOrder;
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43 |
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44 | /**
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45 | * <p>
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46 | * Trie on which the probability calculations are based.
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47 | * </p>
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48 | */
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49 | protected Trie<Event<?>> trie;
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50 |
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51 | /**
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52 | * <p>
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53 | * Random number generator used by probabilistic sequence generation
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54 | * methods.
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55 | * </p>
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56 | */
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57 | protected final Random r;
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58 |
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59 | /**
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60 | * <p>
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61 | * Constructor. Creates a new TrieBasedModel that can be used for stochastic
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62 | * processes with a Markov order less than or equal to {@code markovOrder}.
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63 | * </p>
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64 | *
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65 | * @param markovOrder
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66 | * Markov order of the model
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67 | * @param r
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68 | * random number generator used by probabilistic methods of the
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69 | * class
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70 | */
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71 | public TrieBasedModel(int markovOrder, Random r) {
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72 | super();
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73 | this.trieOrder = markovOrder + 1;
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74 | this.r = r;
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75 | }
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76 |
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77 | /**
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78 | * <p>
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79 | * Trains the model by generating a trie from which probabilities are
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80 | * calculated.
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81 | * </p>
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82 | *
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83 | * @param sequences
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84 | * training data
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85 | */
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86 | public void train(List<List<Event<?>>> sequences) {
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87 | trie = new Trie<Event<?>>();
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88 |
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89 | for (List<Event<?>> sequence : sequences) {
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90 | List<Event<?>> currentSequence = new LinkedList<Event<?>>(sequence); // defensive
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91 | // copy
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92 | currentSequence.add(0, Event.STARTEVENT);
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93 | currentSequence.add(Event.ENDEVENT);
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94 |
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95 | trie.train(currentSequence, trieOrder);
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96 | }
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97 | }
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98 |
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99 | /*
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100 | * (non-Javadoc)
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101 | *
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102 | * @see de.ugoe.cs.eventbench.models.IStochasticProcess#randomSequence()
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103 | */
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104 | @Override
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105 | public List<? extends Event<?>> randomSequence() {
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106 | List<Event<?>> sequence = new LinkedList<Event<?>>();
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107 |
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108 | IncompleteMemory<Event<?>> context = new IncompleteMemory<Event<?>>(
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109 | trieOrder - 1);
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110 | context.add(Event.STARTEVENT);
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111 |
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112 | Event<?> currentState = Event.STARTEVENT;
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113 |
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114 | boolean endFound = false;
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115 |
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116 | while (!endFound) {
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117 | double randVal = r.nextDouble();
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118 | double probSum = 0.0;
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119 | List<Event<?>> currentContext = context.getLast(trieOrder);
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120 | for (Event<?> symbol : trie.getKnownSymbols()) {
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121 | probSum += getProbability(currentContext, symbol);
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122 | if (probSum >= randVal) {
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123 | endFound = (symbol == Event.ENDEVENT);
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124 | if (!(symbol == Event.STARTEVENT || symbol == Event.ENDEVENT)) {
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125 | // only add the symbol the sequence if it is not START
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126 | // or END
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127 | context.add(symbol);
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128 | currentState = symbol;
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129 | sequence.add(currentState);
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130 | }
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131 | break;
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132 | }
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133 | }
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134 | }
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135 | return sequence;
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136 | }
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137 |
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138 | /**
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139 | * <p>
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140 | * Returns a Dot representation of the internal trie.
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141 | * </p>
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142 | *
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143 | * @return dot representation of the internal trie
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144 | */
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145 | public String getTrieDotRepresentation() {
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146 | return trie.getDotRepresentation();
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147 | }
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148 |
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149 | /**
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150 | * <p>
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151 | * Returns a {@link Tree} of the internal trie that can be used for
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152 | * visualization.
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153 | * </p>
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154 | *
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155 | * @return {@link Tree} depicting the internal trie
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156 | */
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157 | public Tree<TrieVertex, Edge> getTrieGraph() {
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158 | return trie.getGraph();
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159 | }
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160 |
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161 | /**
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162 | * <p>
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163 | * The string representation of the model is {@link Trie#toString()} of
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164 | * {@link #trie}.
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165 | * </p>
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166 | *
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167 | * @see java.lang.Object#toString()
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168 | */
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169 | @Override
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170 | public String toString() {
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171 | return trie.toString();
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172 | }
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173 |
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174 | /*
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175 | * (non-Javadoc)
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176 | *
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177 | * @see de.ugoe.cs.eventbench.models.IStochasticProcess#getNumStates()
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178 | */
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179 | @Override
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180 | public int getNumStates() {
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181 | return trie.getNumSymbols();
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182 | }
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183 |
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184 | /*
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185 | * (non-Javadoc)
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186 | *
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187 | * @see de.ugoe.cs.eventbench.models.IStochasticProcess#getStateStrings()
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188 | */
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189 | @Override
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190 | public String[] getStateStrings() {
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191 | String[] stateStrings = new String[getNumStates()];
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192 | int i = 0;
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193 | for (Event<?> symbol : trie.getKnownSymbols()) {
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194 | stateStrings[i] = symbol.toString();
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195 | i++;
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196 | }
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197 | return stateStrings;
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198 | }
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199 |
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200 | /*
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201 | * (non-Javadoc)
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202 | *
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203 | * @see de.ugoe.cs.eventbench.models.IStochasticProcess#getEvents()
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204 | */
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205 | @Override
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206 | public Set<? extends Event<?>> getEvents() {
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207 | return trie.getKnownSymbols();
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208 | }
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209 |
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210 | /*
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211 | * (non-Javadoc)
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212 | *
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213 | * @see
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214 | * de.ugoe.cs.eventbench.models.IStochasticProcess#generateSequences(int)
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215 | */
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216 | @Override
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217 | public Set<List<? extends Event<?>>> generateSequences(int length) {
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218 | return generateSequences(length, false);
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219 | }
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220 |
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221 | /*
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222 | * (non-Javadoc)
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223 | *
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224 | * @see
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225 | * de.ugoe.cs.eventbench.models.IStochasticProcess#generateSequences(int,
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226 | * boolean)
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227 | */
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228 | @Override
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229 | public Set<List<? extends Event<?>>> generateSequences(int length,
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230 | boolean fromStart) {
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231 | Set<List<? extends Event<?>>> sequenceSet = new LinkedHashSet<List<? extends Event<?>>>();
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232 | ;
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233 | if (length < 1) {
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234 | throw new InvalidParameterException(
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235 | "Length of generated subsequences must be at least 1.");
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236 | }
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237 | if (length == 1) {
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238 | if (fromStart) {
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239 | List<Event<?>> subSeq = new LinkedList<Event<?>>();
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240 | subSeq.add(Event.STARTEVENT);
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241 | sequenceSet.add(subSeq);
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242 | } else {
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243 | for (Event<?> event : getEvents()) {
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244 | List<Event<?>> subSeq = new LinkedList<Event<?>>();
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245 | subSeq.add(event);
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246 | sequenceSet.add(subSeq);
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247 | }
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248 | }
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249 | return sequenceSet;
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250 | }
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251 | Set<? extends Event<?>> events = getEvents();
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252 | Set<List<? extends Event<?>>> seqsShorter = generateSequences(
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253 | length - 1, fromStart);
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254 | for (Event<?> event : events) {
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255 | for (List<? extends Event<?>> seqShorter : seqsShorter) {
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256 | Event<?> lastEvent = event;
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257 | if (getProbability(seqShorter, lastEvent) > 0.0) {
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258 | List<Event<?>> subSeq = new ArrayList<Event<?>>(seqShorter);
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259 | subSeq.add(lastEvent);
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260 | sequenceSet.add(subSeq);
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261 | }
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262 | }
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263 | }
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264 | return sequenceSet;
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265 | }
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266 |
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267 | /*
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268 | * (non-Javadoc)
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269 | *
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270 | * @see
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271 | * de.ugoe.cs.eventbench.models.IStochasticProcess#generateValidSequences
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272 | * (int)
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273 | */
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274 | @Override
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275 | public Set<List<? extends Event<?>>> generateValidSequences(int length) {
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276 | // check for min-length implicitly done by generateSequences
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277 | Set<List<? extends Event<?>>> allSequences = generateSequences(length,
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278 | true);
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279 | Set<List<? extends Event<?>>> validSequences = new LinkedHashSet<List<? extends Event<?>>>();
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280 | for (List<? extends Event<?>> sequence : allSequences) {
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281 | if (sequence.size() == length
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282 | && Event.ENDEVENT.equals(sequence.get(sequence.size() - 1))) {
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283 | validSequences.add(sequence);
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284 | }
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285 | }
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286 | return validSequences;
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287 | }
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288 |
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289 | } |
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