Java tutorial
/* * Copyright 2007-2010 Tom Castle & Lawrence Beadle * Licensed under GNU General Public License * * This file is part of EpochX: genetic programming software for research * * EpochX is free software: you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation, either version 3 of the License, or * (at your option) any later version. * * EpochX is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with EpochX. If not, see <http://www.gnu.org/licenses/>. * * The latest version is available from: http:/www.epochx.org */ package org.epochx.ge.model.epox; import org.apache.commons.lang.ArrayUtils; import org.epochx.ge.model.GEModel; import org.epochx.ge.representation.GECandidateProgram; import org.epochx.representation.CandidateProgram; import org.epochx.tools.eval.*; import org.epochx.tools.grammar.Grammar; import org.epochx.tools.util.BoolUtils; /** * Grammar model for the multiplexer problems using an Epox grammar. * * <h4>Multiplexer problem</h4> * * Given n binary inputValues, a program that solves the majority problem will * return true in all circumstances where a majority of the inputValues are true * (or 1), and return false whenever there is not a majority of true values. */ public class Multiplexer extends GEModel { // Incomplete grammar requiring correct number of terminals to be added. private static final String GRAMMAR_FRAGMENT = "<prog> ::= <node>\n" + "<node> ::= <function> | <terminal>\n" + "<function> ::= NOT( <node> ) " + "| OR( <node> , <node> ) " + "| AND( <node> , <node> ) " + "| IF( <node> , <node> , <node> )\n" + "<terminal> ::= "; // Epox interpreter for performing evaluation. private final EpoxInterpreter interpreter; // The boolean input sequences. private final boolean[][] inputValues; // The names of the inputValues used in the grammar. private String[] argNames; // No input bits. private int noAddressBits; private int noDataBits; /** * Constructs a Multiplexer model for the given number of inputs. * * @param noInputBits the number of inputs the multiplexer problem should be * for */ public Multiplexer(final int noInputBits) { interpreter = new EpoxInterpreter(); // Generate the input sequences. inputValues = BoolUtils.generateBoolSequences(noInputBits); // Calculate number of address/data bits. setBitSizes(noInputBits); // Determine the input argument names. setArgNames(noInputBits); // Complete the grammar string and construct grammar instance. setGrammar(new Grammar(getGrammarString())); } /** * Calculates the fitness score for the given program. The fitness of a * program for the majority problem is calculated by evaluating it * using each of the possible sets of input values. There are * <code>2^noInputBits</code> possible sets of inputs. The fitness of the * program is the quantity of those input sequences that the program * returned an incorrect response for. That is, a fitness value of * <code>0.0</code> indicates the program responded correctly for every * possible set of input values. * * @param p {@inheritDoc} * @return the calculated fitness for the given program. */ @Override public double getFitness(final CandidateProgram p) { final GECandidateProgram program = (GECandidateProgram) p; double score = 0; // Evaluate all possible inputValues. for (final boolean[] vars : inputValues) { // Convert to object array. final Boolean[] objVars = ArrayUtils.toObject(vars); Boolean result = null; try { result = (Boolean) interpreter.eval(program.getSourceCode(), argNames, objVars); } catch (final MalformedProgramException e) { // Assign worst possible fitness and stop evaluating. score = 0; break; } if ((result != null) && (result == multiplex(vars))) { score++; } } return inputValues.length - score; } /** * Constructs and returns the full grammar string for the multiplexer * problem with the correct number of address and data bits. * * @return the grammar string for the multiplexer problem with the set * number of input bits */ public String getGrammarString() { final StringBuilder buffer = new StringBuilder(GRAMMAR_FRAGMENT); for (int i = 0; i < argNames.length; i++) { if (i > 0) { buffer.append(" | "); } buffer.append(argNames[i]); } buffer.append('\n'); return buffer.toString(); } /* * Calculate and set the number of address and data bits. */ private void setBitSizes(final int noInputBits) { noAddressBits = 1; while (true) { noDataBits = (int) Math.pow(2, noAddressBits); if ((noAddressBits + noDataBits) == noInputBits) { break; } noAddressBits++; } } /* * Set the argument names for the inputs. */ private void setArgNames(final int noInputBits) { argNames = new String[noInputBits]; // Add address inputs. for (int i = 0; i < noAddressBits; i++) { argNames[i] = "a" + i; } // Add data inputs. for (int i = noAddressBits; i < noInputBits; i++) { argNames[i] = "d" + i; } } /* * Calculate what the correct response should be for the given inputs. */ private Boolean multiplex(final boolean[] vars) { // Calculate which data position to use. int dataPosition = 0; for (int i = 0; i < noAddressBits; i++) { if (vars[i]) { dataPosition += Math.pow(2, i); } } return vars[noAddressBits + dataPosition]; } }