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lib/Algorithm/Evolutionary/Op/GaussianMutation.pm  view on Meta::CPAN

=head2 new( [$average = 0] [, $standard deviation = 1] [, $rate = 1 ]

Creates a new mutation operator with an application rate. Rate defaults to 1.

=cut

sub new {
  my $class = shift;
  my $avg = shift || 0; 
  my $stddev = shift || 1;
  my $rate = shift || 1;

  my $hash = {avg => $avg,
	      stddev => $stddev };
  my $self = Algorithm::Evolutionary::Op::Base::new( 'Algorithm::Evolutionary::Op::GaussianMutation', $rate, $hash );
  return $self;
}

=head2 create

Creates a new mutation operator with an application rate. Rate defaults to 0.1.

Called create to distinguish from the classwide ctor, new. It just
makes simpler to create a Mutation Operator

=cut

sub create {
  my $class = shift;
  my $avg = shift || 0; 
  my $stddev = shift || 1;
  
  my $self = {_avg => $avg,
	      _stddev => $stddev };

  bless $self, $class;
  return $self;
}

=head2 apply( $chromosome )

Applies mutation operator to a "Chromosome", a vector of stuff,
really. Can be applied only to I<victims> with the C<_array> instance
variable; but it checks before application (roughly) that the operand is of
type L<Algorithm::Evolutionary::Individual::Vector>.

=cut

sub apply ($$) {
  my $self = shift;
  my $arg = shift || croak "No victim here!";
  croak "Incorrect type".(ref $arg) if !$arg->{_array};
  my $victim = clone($arg);
  my @deltas = random_normal( @{$victim->{_array}} + 1,  #+1 is needed, returns empty if not
			      $self->{_avg}, $self->{_stddev} );
  for ( @{$victim->{_array}} ) {
      my $adjust = pop @deltas;
      $_ += $adjust;
      # makes sure that the new value stays within its confines
      if($_ < $victim->{_rangestart}) {
	  $_ = $victim->{_rangestart};
      } elsif($_ > $victim->{_rangeend}) {
	  $_ = $victim->{_rangeend};
      }
  }
  $victim->{_fitness} = undef;
  return $victim;
}

=head1 THANKS

This file has been improved with input from Christoph Meißner.

=head1 Copyright
  
  This file is released under the GPL. See the LICENSE file included in this distribution,
  or go to http://www.fsf.org/licenses/gpl.txt

=cut