Provided by: libmath-combinatorics-perl_0.09-4_all bug

NAME

       Math::Combinatorics - Perform combinations and permutations on lists

SYNOPSIS

       Available as an object oriented API.

         use Math::Combinatorics;

         my @n = qw(a b c);
         my $combinat = Math::Combinatorics->new(count => 2,
                                                 data => [@n],
                                                );

         print "combinations of 2 from: ".join(" ",@n)."\n";
         print "------------------------".("--" x scalar(@n))."\n";
         while(my @combo = $combinat->next_combination){
           print join(' ', @combo)."\n";
         }

         print "\n";

         print "permutations of 3 from: ".join(" ",@n)."\n";
         print "------------------------".("--" x scalar(@n))."\n";
         while(my @permu = $combinat->next_permutation){
           print join(' ', @permu)."\n";
         }

         output:

       Or available via exported functions 'permute', 'combine', and 'factorial'.

         use Math::Combinatorics;

         my @n = qw(a b c);
         print "combinations of 2 from: ".join(" ",@n)."\n";
         print "------------------------".("--" x scalar(@n))."\n";
         print join("\n", map { join " ", @$_ } combine(2,@n)),"\n";
         print "\n";
         print "permutations of 3 from: ".join(" ",@n)."\n";
         print "------------------------".("--" x scalar(@n))."\n";
         print join("\n", map { join " ", @$_ } permute(@n)),"\n";

       Output:

         combinations of 2 from: a b c
         ------------------------------
         a b
         a c
         b c

         permutations of 3 from: a b c
         ------------------------------
         a b c
         a c b
         b a c
         b c a
         c a b
         c b a

       Output from both types of calls is the same, but the object-oriented approach consumes
       much less memory for large sets.

DESCRIPTION

       Combinatorics is the branch of mathematics studying the enumeration, combination, and
       permutation of sets of elements and the mathematical relations that characterize their
       properties.  As a jumping off point, refer to:

        http://mathworld.wolfram.com/Combinatorics.html

       This module provides a pure-perl implementation of nCk, nCRk, nPk, nPRk, !n and n!
       (combination, multiset, permutation, string, derangement, and factorial, respectively).
       Functional and object-oriented usages allow problems such as the following to be solved:

       combine - nCk
            http://mathworld.wolfram.com/Combination.html

           "Fun questions to ask the pizza parlor wait staff: how many possible combinations of 2
           toppings can I get on my pizza?".

       derange - !n
            http://mathworld.wolfram.com/Derangement.html

           "A derangement of n ordered objects, denoted !n, is a permutation in which none of the
           objects appear in their "natural" (i.e., ordered) place."

       permute - nPk
            http://mathworld.wolfram.com/Permutation.html

           "Master Mind Game: ways to arrange pieces of different colors in a certain number of
           positions, without repetition of a color".

       Object-oriented usage additionally allows solving these problems by calling "new()" with a
       frequency vector:

       string - nPRk
            http://mathworld.wolfram.com/String.html

           "Morse signals: diferent signals of 3 positions using the two symbols - and .".

            $o = Math::Combinatorics->new( count=>3 , data=>[qw(. -)] , frequency=>[3,3] );
            while ( my @x = $o->next_multiset ) {
              my $p = Math::Combinatorics->new( data=>\@x , frequency=>[map{1} @x] );
              while ( my @y = $p->next_string ) {
                #do something
              }
            }

       multiset/multichoose - nCRk
            http://mathworld.wolfram.com/Multiset.html

           "ways to extract 3 balls at once of a bag with 3 black and 3 white balls".

            $o = Math::Combinatorics->new( count=>3 , data=>[qw(white black)] , frequency=>[3,3] );
            while ( my @x = $o->next_multiset ) {
              #do something
            }

   EXPORT
       the following export tags will bring a single method into the caller's namespace.  no
       symbols are exported by default.  see pod documentation below for method descriptions.

         combine
         derange
         multiset
         permute
         string
         factorial

AUTHOR

       Allen Day <allenday@ucla.edu>, with algorithmic contributions from Christopher Eltschka
       and Tye.

       Copyright (c) 2004-2005 Allen Day. All rights reserved. This program is free software; you
       can redistribute it and/or modify it under the same terms as Perl itself.

ACKNOWLEDGEMENTS

       A sincere thanks to everyone for helping to make this a better module.  After initial
       development I've only had time to accept patches and improvements.  Math::Combinatorics
       continues to be developed and improved by the community.  Contributors of note include:

       For adding new features: Carlos Rica, David Coppit, Carlos Segre, Lyon Lemmens

       For bug reports: Ying Yang, Joerg Beyer, Marc Logghe, Yunheng Wang, Torsten Seemann,
       Gerrit Haase, Joern Behre, Lyon Lemmens, Federico Lucifredi

BUGS / TODO

       Report them to the author.

        * Need more extensive unit tests.

          * tests for new()'s frequency argment

        * A known bug (more of a missing feature, actually) does not allow parameterization of k
        for nPk in permute().  it is assumed k == n.  L</permute()> for details.  You can work
        around this by making calls to both L</permute()> and L</combine()>

        * Lots of really interesting stuff from Mathworld.Wolfram.com.  MathWorld rocks!  Expect
        to see implementation of more concepts from their site, e.g.:

          http://mathworld.wolfram.com/BellNumber.html
          http://mathworld.wolfram.com/StirlingNumberoftheSecondKind.html
          http://mathworld.wolfram.com/Word.html

        * Other combinatorics stuff
          http://en.wikipedia.org/wiki/Catalan_number
          http://en.wikipedia.org/wiki/Stirling_number

SEE ALSO

       Set::Scalar

       Set::Bag

       String::Combination (alas misnamed, it actually returns permutations on a string).

        http://perlmonks.thepen.com/29374.html

        http://groups.google.com/groups?selm=38568F79.13680B86%40physik.tu-muenchen.de&output=gplain

EXPORTED FUNCTIONS

   combine()
        Usage   : my @combinations = combine($k,@n);
        Function: implements nCk (n choose k), or n!/(k!*(n-k!)).
                  returns all unique unorderd combinations of k items from set n.
                  items in n are assumed to be character data, and are
                  copied into the return data structure (see "Returns" below).
        Example : my @n = qw(a b c);
                  my @c = combine(2,@n);
                  print join "\n", map { join " ", @$_ } @c;
                  # prints:
                  # b c
                  # a c
                  # a b
        Returns : a list of arrays, where each array contains a unique combination
                  of k items from n
        Args    : a list of items to be combined
        Notes   : data is internally assumed to be alphanumeric.  this is necessary
                  to efficiently generate combinations of large sets.  if you need
                  combinations of non-alphanumeric data, or on data
                  C<sort {$a cmp $b}> would not be appropriate, use the
                  object-oriented API.  See L</new()> and the B<compare> option.

                  Identical items are assumed to be non-unique.  That is, calling
                  C<combine(1,'a','a') yields two sets: {a}, and {a}.  See
                  L</next_multiset() if this is not the desired behavior.

   derange()
        Usage   : my @deranges = derange(@n);
        Function: implements !n, a derangement of n items in which none of the
                  items appear in their originally ordered place.
        Example : my @n = qw(a b c);
                  my @d = derange(@n);
                  print join "\n", map { join " ", @$_ } @d;
                  # prints:
                  # a c b
                  # b a c
                  # b c a
                  # c a b
                  # c b a
        Returns : a list of arrays, where each array contains a derangement of
                  k items from n (where k == n).
        Args    : a list of items to be deranged.
        Note    : k should really be parameterizable.  this will happen
                  in a later version of the module.  send me a patch to
                  make that version come out sooner.
        Notes   : data is internally assumed to be alphanumeric.  this is necessary
                  to efficiently generate combinations of large sets.  if you need
                  combinations of non-alphanumeric data, or on data
                  C<sort {$a cmp $b}> would not be appropriate, use the
                  object-oriented API.  See L</new()>, and the B<compare> option.

   next_derangement()
        Usage   : my @derangement = $c->next_derangement();
        Function: get derangements for @data.
        Returns : returns a permutation of items from @data (see L</new()>),
                  where none of the items appear in their natural order.  repeated calls
                  retrieve all unique derangements of @data elements.  a returned empty
                  list signifies all derangements have been iterated.
        Args    : none.

   factorial()
        Usage   : my $f = factorial(4); #returns 24, or 4*3*2*1
        Function: calculates n! (n factorial).
        Returns : undef if n is non-integer or n < 0
        Args    : a positive, non-zero integer
        Note    : this function is used internally by combine() and permute()

   permute()
        Usage   : my @permutations = permute(@n);
        Function: implements nPk (n permute k) (where k == n), or n!/(n-k)!
                   returns all unique permutations of k items from set n
                  (where n == k, see "Note" below).  items in n are assumed to
                  be character data, and are copied into the return data
                  structure.
        Example : my @n = qw(a b c);
                  my @p = permute(@n);
                  print join "\n", map { join " ", @$_ } @p;
                  # prints:
                  # b a c
                  # b c a
                  # c b a
                  # c a b
                  # a c b
                  # a b c
        Returns : a list of arrays, where each array contains a permutation of
                  k items from n (where k == n).
        Args    : a list of items to be permuted.
        Note    : k should really be parameterizable.  this will happen
                  in a later version of the module.  send me a patch to
                  make that version come out sooner.
        Notes   : data is internally assumed to be alphanumeric.  this is necessary
                  to efficiently generate combinations of large sets.  if you need
                  combinations of non-alphanumeric data, or on data
                  C<sort {$a cmp $b}> would not be appropriate, use the
                  object-oriented API.  See L</new()>, and the B<compare> option.

                  Identical items are assumed to be non-unique.  That is, calling
                  C<permute('a','a') yields two sets: {a,a}, and {a,a}.  See
                  L</next_string() if this is not the desired behavior.

CONSTRUCTOR

   new()
        Usage   : my $c = Math::Combinatorics->new( count => 2,       #treated as int
                                                    data => [1,2,3,4] #arrayref or anonymous array
                                                  );
        Function: build a new Math::Combinatorics object.
        Returns : a Math::Combinatorics object
        Args    : count     - required for combinatoric functions/methods.  number of elements to be
                              present in returned set(s).
                  data      - required for combinatoric B<AND> permutagenic functions/methods.  this is the
                              set elements are chosen from.  B<NOTE>: this array is modified in place; make
                              a copy of your array if the order matters in the caller's space.
                  frequency - optional vector of data frequencies.  must be the same length as the B<data>
                              constructor argument.  These two constructor calls here are equivalent:

                                $a = 'a';
                                $b = 'b';

                                Math::Combinatorics->new( count=>2, data=>[\$a,\$a,\$a,\$a,\$a,\$b,\$b] );
                                Math::Combinatorics->new( count=>2, data=>[\$a,\$b], frequency=>[5,2] );

                              so why use this?  sometimes it's useful to have multiple identical entities in
                              a set (in set theory jargon, this is called a "bag", See L<Set::Bag>).
                  compare   - optional subroutine reference used in sorting elements of the set.  examples:

                              #appropriate for character elements
                              compare => sub { $_[0] cmp $_[1] }
                              #appropriate for numeric elements
                              compare => sub { $_[0] <=> $_[1] }
                              #appropriate for object elements, perhaps
                              compare => sub { $_[0]->value <=> $_[1]->value }

                            The default sort mechanism is based on references, and cannot be predicted.
                            Improvements for a more flexible compare() mechanism are most welcome.

OBJECT METHODS

   next_combination()
        Usage   : my @combo = $c->next_combination();
        Function: get combinations of size $count from @data.
        Returns : returns a combination of $count items from @data (see L</new()>).
                  repeated calls retrieve all unique combinations of $count elements.
                  a returned empty list signifies all combinations have been iterated.
        Note    : this method may only be used if a B<frequency> argument is B<NOT>
                  given to L</new()>, otherwise use L</next_multiset()>.
        Args    : none.

   next_multiset()
        Usage   : my @multiset = $c->next_multiset();
        Function: get multisets for @data.
        Returns : returns a multiset of items from @data (see L</new()>).
                  a multiset is a special type of combination where the set from which
                  combinations are drawn contains items that are indistinguishable.  use
                  L</next_multiset()> when a B<frequency> argument is passed to L</new()>.
                  repeated calls retrieve all unique multisets of @data elements.  a
                  returned empty list signifies all multisets have been iterated.
        Note    : this method may only be used if a B<frequency> argument is given to
                  L</new()>, otherwise use L</next_combination()>.
        Args    : none.

   next_permutation()
        Usage   : my @permu = $c->next_permutation();
        Function: get permutations of elements in @data.
        Returns : returns a permutation of items from @data (see L</new()>).
                  repeated calls retrieve all unique permutations of @data elements.
                  a returned empty list signifies all permutations have been iterated.
        Note    : this method may only be used if a B<frequency> argument is B<NOT>
                  given to L</new()>, otherwise use L</next_string()>.
        Args    : none.

   next_string()
        Usage   : my @string = $c->next_string();
        Function: get strings for @data.
        Returns : returns a multiset of items from @data (see L</new()>).
                  a multiset is a special type of permutation where the set from which
                  combinations are drawn contains items that are indistinguishable.  use
                  L</next_permutation()> when a B<frequency> argument is passed to L</new()>.
                  repeated calls retrieve all unique multisets of @data elements.  a
                  returned empty list signifies all strings have been iterated.
        Note    : this method may only be used if a B<frequency> argument is given to
                  L</new()>, otherwise use L</next_permutation()>.
        Args    : none.

INTERNAL FUNCTIONS AND METHODS

   sum()
        Usage   : my $sum = sum(1,2,3); # returns 6
        Function: sums a list of integers.  non-integer list elements are ignored
        Returns : sum of integer items in arguments passed in
        Args    : a list of integers
        Note    : this function is used internally by combine()

   compare()
        Usage   : $obj->compare()
        Function: internal, undocumented.  holds a comparison coderef.
        Returns : value of compare (a coderef)

   count()
        Usage   : $obj->count()
        Function: internal, undocumented.  holds the "k" in nCk or nPk.
        Returns : value of count (an int)

   data()
        Usage   : $obj->data()
        Function: internal, undocumented.  holds the set "n" in nCk or nPk.
        Returns : value of data (an arrayref)

   swap()
       internal, undocumented.

   reverse()
       internal, undocumented.

   rotate()
       internal, undocumented.

   upper_bound()
       internal, undocumented.

   lower_bound()
       internal, undocumented.

   _permutation_cursor()
        Usage   : $obj->_permutation_cursor()
        Function: internal method.  cursor on permutation iterator order.
        Returns : value of _permutation_cursor (an arrayref)
        Args    : none