1 | package de.ugoe.cs.eventbench.models;
|
---|
2 |
|
---|
3 | import java.util.LinkedList;
|
---|
4 | import java.util.List;
|
---|
5 | import java.util.Random;
|
---|
6 |
|
---|
7 | import de.ugoe.cs.eventbench.data.Event;
|
---|
8 |
|
---|
9 | /**
|
---|
10 | * <p>
|
---|
11 | * Implements a Deterministic Finite Automata (DFA) capable of random session
|
---|
12 | * generation. It is a special case of a first-order Markov model, where the
|
---|
13 | * transition probability is equally high for all following states.
|
---|
14 | * </p>
|
---|
15 | *
|
---|
16 | * @author Steffen Herbold
|
---|
17 | * @version 1.0
|
---|
18 | */
|
---|
19 | public class DeterministicFiniteAutomaton extends FirstOrderMarkovModel {
|
---|
20 |
|
---|
21 | /**
|
---|
22 | * <p>
|
---|
23 | * Id for object serialization.
|
---|
24 | * </p>
|
---|
25 | */
|
---|
26 | private static final long serialVersionUID = 1L;
|
---|
27 |
|
---|
28 | /**
|
---|
29 | * <p>
|
---|
30 | * Constructor. Creates a new DeterministicFiniteAutomaton.
|
---|
31 | * </p>
|
---|
32 | *
|
---|
33 | * @param r
|
---|
34 | * random number generator used by probabilistic methods of the
|
---|
35 | * class
|
---|
36 | */
|
---|
37 | public DeterministicFiniteAutomaton(Random r) {
|
---|
38 | super(r);
|
---|
39 | }
|
---|
40 |
|
---|
41 | /**
|
---|
42 | * <p>
|
---|
43 | * Calculates the proability of the next state. Each of the following states
|
---|
44 | * in the automaton is equally probable.
|
---|
45 | * </p>
|
---|
46 | *
|
---|
47 | * @see de.ugoe.cs.eventbench.models.IStochasticProcess#getProbability(java.util.List,
|
---|
48 | * de.ugoe.cs.eventbench.data.Event)
|
---|
49 | */
|
---|
50 | @Override
|
---|
51 | public double getProbability(List<? extends Event<?>> context,
|
---|
52 | Event<?> symbol) {
|
---|
53 | double result = 0.0d;
|
---|
54 |
|
---|
55 | List<Event<?>> contextCopy;
|
---|
56 | if (context.size() >= trieOrder) {
|
---|
57 | contextCopy = new LinkedList<Event<?>>(context.subList(
|
---|
58 | context.size() - trieOrder + 1, context.size()));
|
---|
59 | } else {
|
---|
60 | contextCopy = new LinkedList<Event<?>>(context);
|
---|
61 | }
|
---|
62 |
|
---|
63 | List<Event<?>> followers = trie.getFollowingSymbols(contextCopy);
|
---|
64 |
|
---|
65 | if (followers.size() != 0 && followers.contains(symbol)) {
|
---|
66 | result = 1.0d / followers.size();
|
---|
67 | }
|
---|
68 |
|
---|
69 | return result;
|
---|
70 | }
|
---|
71 |
|
---|
72 | }
|
---|