Przemysław Wesołek > Data-Pareto-0.05 > Data::Pareto

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NAME ^

Data::Pareto - Computing Pareto sets in Perl

VERSION ^

Version 0.05

SYNOPSIS ^

  use Data::Pareto;
  
  # only first and third columns are used in comparison
  # the others are simply descriptive
  my $set = new Data::Pareto( { columns => [0, 2] } );
  $set->add(
      [ 5, "pareto", 10, 11 ],
      [ 5, "dominated", 11, 9 ],
      [ 4, "pareto2", 12, 12 ] 
  );

  # this returns [ [ 5, "pareto", 10, 11 ], [ 4, "pareto2", 12, 12 ] ],
  # the other one is dominated on selected columns
  $set->get_pareto_ref;

DESCRIPTION ^

This module makes calculation of Pareto set. Given a set of vectors (i.e. arrays of simple scalars), Pareto set is all the vectors from the given set which are not dominated by any other vector of the set. A vector X is said to be dominated by Y, iff X[i] >= Y[i] for all i and X[i] > Y[i] for at least one i.

Pareto sets play an important role in multiobjective optimization, where each non-dominated (i.e. Pareto) vector describes objectives value of "optimal" solution to the given problem.

This module allows occurrence of duplicates in the set - this makes it rather a bag than a set, but is useful in practice (e.g. when we want to preserve two solutions giving the same objectives value, but structurally different). This assumption influences dominance definition given above: two duplicates never dominate each other and hence can be present in the Pareto set. This is controlled by duplicates option passed to new(): if set to true value, duplicates are allowed in Pareto set; otherwise, only the first found element of the subset of duplicated vectors is preserved in Pareto set.

The values are allowed to be invalid. The meaning of 'invalid' is 'the worst possible'. It's different concept than 'unknown'; unknown value make the definition of domination less clear.

By default, the comparison of column values is numerical and the smaller value dominates the larger one. If you want to override this behaviour, pass your own dominator sub in arguments to new().

FUNCTIONS ^

By default, a vector is passed around as a ref to array of consecutive column values. This means you shouldn't mess with it after passing to add method.

new

Creates a new object for calculating Pareto set.

The first argument passed is a hashref with options; the recognized options are:

The rest of arguments are assumed to be vectors, and passed to add() method.

add

Tests vectors passed as arguments and adds the non-dominated ones to the Pareto set.

get_pareto

Returns the current content of Pareto set as a list of vectors.

get_pareto_ref

Returns the current content of Pareto set as a ref to array with vectors. The return value references the original array, so treat it as read-only!

is_dominated

Checks if the first vector passed is dominated by the second one. The comparison is made based on the values in vectors' columns, which were passed to new().

The vectors passed are never duplicates of each other when this method is called from inside this module.

Returns true, when the first vector from arguments list is dominated by the other one, and false otherwise.

is_invalid

Checks if the given value is considered invalid for the current object. Every value is valid by default.

TODO ^

Allow specifying built-in dominators inside dominator hash.

For large data sets calculations become time-intensive. There are a couple of techniques which might be applied to improve the performance:

AUTHOR ^

Przemyslaw Wesolek, <jest at go.art.pl>

BUGS ^

Please report any bugs or feature requests to bug-data-pareto at rt.cpan.org, or through the web interface at http://rt.cpan.org/NoAuth/ReportBug.html?Queue=Data-Pareto. I will be notified, and then you'll automatically be notified of progress on your bug as I make changes.

SUPPORT ^

You can find documentation for this module with the perldoc command.

    perldoc Data::Pareto

You can also look for information at:

COPYRIGHT & LICENSE ^

Copyright 2009 Przemyslaw Wesolek

This program is free software; you can redistribute it and/or modify it under the terms of the Artistic License 2.0. For details, see the full text of the license in the file LICENSE.

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