1use strict; 2use warnings; 3 4=head1 NAME 5 6 Algorithm::Evolutionary::Op::NoChangeTerm - Checks for termination of an algorithm; terminates 7 when several generations transcur without change 8 9=head1 SYNOPSIS 10 11 my $nct = new Algorithm::Evolutionary::Op::NoChangeTerm 10; 12 #nct->apply( \@pop ) will return false after 10 generations w/o change 13 14=head1 Base Class 15 16L<Algorithm::Evolutionary::Op::Base|Algorithm::Evolutionary::Op::Base> 17 18=head1 DESCRIPTION 19 20Algorithm::Evolutionary::Op::NoChangeTerm is used when we want an 21algorithm to finish when the population has stagnated, or the global 22optimum is found. It counts how many generations the population has 23not changed, and returns false after that limit is reached. 24 25It is useful if you want to run an algorithm for a certain time, or if 26you want to apply some fancy diversity operator 27 28=head1 METHODS 29 30=cut 31 32package Algorithm::Evolutionary::Op::NoChangeTerm; 33 34our ($VERSION) = ( '$Revision: 3.0 $ ' =~ / (\d+\.\d+)/ ) ; 35 36use base 'Algorithm::Evolutionary::Op::Base'; 37 38=head2 new( [$number_of_generations_without_change] ) 39 40Creates a new terminator. Takes as an argument the number of 41generations after which it will return false, which defaults to 10. 42 43=cut 44 45sub new { 46 my $class = shift; 47 my $hash = { noChangeCounterMax => shift || 10, 48 noChangeCounter => 0, 49 lastBestFitness => rand()}; # A random value, unlikely 50 # to be matched 51 my $self = Algorithm::Evolutionary::Op::Base::new( __PACKAGE__, 1, $hash ); 52 return $self; 53} 54 55 56=head2 apply( $population ) 57 58Checks if the first member of the population has the same fitness as before, 59and increments counter. The population I<should be ordered> 60 61=cut 62 63sub apply ($) { 64 my $self = shift; 65 my $pop = shift; 66 67 if ( $pop->[0]->Fitness() == $self->{_lastBestFitness} ) { 68 $self->{_noChangeCounter}++; 69# print "NCT => ", $self->{_noChangeCounter}++, "\n"; 70 } else { 71 $self->{_lastBestFitness}= $pop->[0]->Fitness(); 72 $self->{_noChangeCounter} = 0; 73 } 74 return $self->{_noChangeCounter} < $self->{_noChangeCounterMax}; 75 76} 77 78=head1 See Also 79 80L<Algorithm::Evolutionary::Op::FullAlgorithm> needs an object of this class to check 81for the termination condition. It's normally used alongside "generation-type" 82objects such as L<Algorithm::Evolutionary::Op::Easy>. 83 84There are other options for termination conditions: L<Algorithm::Evolutionary::Op::DeltaTerm> and 85L<Algorithm::Evolutionary::Op::GenerationalTerm>. 86 87 88=head1 Copyright 89 90 This file is released under the GPL. See the LICENSE file included in this distribution, 91 or go to http://www.fsf.org/licenses/gpl.txt 92 93 CVS Info: $Date: 2009/07/24 08:46:59 $ 94 $Header: /media/Backup/Repos/opeal/opeal/Algorithm-Evolutionary/lib/Algorithm/Evolutionary/Op/NoChangeTerm.pm,v 3.0 2009/07/24 08:46:59 jmerelo Exp $ 95 $Author: jmerelo $ 96 $Revision: 3.0 $ 97 $Name $ 98 99=cut 100 101"The truth is out there"; 102