[comment {-*- tcl -*- doctools manpage}]
[manpage_begin math::combinatorics n 2.1]
[moddesc   {Tcl Math Library}]
[titledesc {Combinatorial functions in the Tcl Math Library}]
[category  Mathematics]
[require Tcl "8.5 9"]
[require math [opt 1.2.6]]
[require Tcl "8.6 9"]
[require TclOO]
[require math::combinatorics [opt 2.1]]
[description]
[para]

The [package math] package contains implementations of several
functions useful in combinatorial problems. The [package math::combinatorics]
extends the collections based on features in Tcl 8.6.

Note: the meaning of the partitionP function, Catalan and Stirling numbers is explained on the
[uri http://mathworld.wolfram.com {MathWorld website}]


[section COMMANDS]
[list_begin definitions]

[call [cmd ::math::ln_Gamma] [arg z]]

Returns the natural logarithm of the Gamma function for the argument
[arg z].

[para]

The Gamma function is defined as the improper integral from zero to
positive infinity of

[example {
  t**(x-1)*exp(-t) dt
}]

[para]

The approximation used in the Tcl Math Library is from Lanczos,
[emph {ISIAM J. Numerical Analysis, series B,}] volume 1, p. 86.
For "[var x] > 1", the absolute error of the result is claimed to be
smaller than 5.5*10**-10 -- that is, the resulting value of Gamma when

[example {
  exp( ln_Gamma( x) )
}]

is computed is expected to be precise to better than nine significant
figures.

[call [cmd ::math::factorial] [arg x]]

Returns the factorial of the argument [arg x].

[para]

For integer [arg x], 0 <= [arg x] <= 12, an exact integer result is
returned.

[para]

For integer [arg x], 13 <= [arg x] <= 21, an exact floating-point
result is returned on machines with IEEE floating point.

[para]

For integer [arg x], 22 <= [arg x] <= 170, the result is exact to 1
ULP.

[para]

For real [arg x], [arg x] >= 0, the result is approximated by
computing [term Gamma(x+1)] using the [cmd ::math::ln_Gamma]
function, and the result is expected to be precise to better than nine
significant figures.

[para]

It is an error to present [arg x] <= -1 or [arg x] > 170, or a value
of [arg x] that is not numeric.

[call [cmd ::math::choose] [arg {n k}]]

Returns the binomial coefficient [term {C(n, k)}]

[example {
   C(n,k) = n! / k! (n-k)!
}]

If both parameters are integers and the result fits in 32 bits, the
result is rounded to an integer.

[para]

Integer results are exact up to at least [arg n] = 34.  Floating point
results are precise to better than nine significant figures.

[call [cmd ::math::Beta] [arg {z w}]]

Returns the Beta function of the parameters [arg z] and [arg w].

[example {
   Beta(z,w) = Beta(w,z) = Gamma(z) * Gamma(w) / Gamma(z+w)
}]

Results are returned as a floating point number precise to better than
nine significant digits provided that [arg w] and [arg z] are both at
least 1.


[call [cmd ::math::combinatorics::permutations] [arg n]]
Return the number of permutations of n items. The returned number
is always an integer, it is not limited by the range of 32-or 64-bits
integers using the arbitrary precision integers available in Tcl 8.5 and later.

[list_begin arguments]
[arg_def int n] The number of items to be permuted.
[list_end]

[call [cmd ::math::combinatorics::variations] [arg n] [arg k]]
Return the number of variations k items selected from the total of n items.
The order of the items is taken into account.

[list_begin arguments]
[arg_def int n] The number of items to be selected from.
[arg_def int k] The number of items to be selected in each variation.
[list_end]

[call [cmd ::math::combinatorics::combinations] [arg n] [arg k]]
Return the number of combinations of k items selected from the total of n items.
The order of the items is not important.

[list_begin arguments]
[arg_def int n] The number of items to be selected from.
[arg_def int k] The number of items to be selected in each combination.
[list_end]

[call [cmd ::math::combinatorics::derangements] [arg n]]
Return the number of derangements of n items. A derangement is a permutation
where each item is displaced from the original position.

[list_begin arguments]
[arg_def int n] The number of items to be rearranged.
[list_end]

[call [cmd ::math::combinatorics::catalan] [arg n]]
Return the n'th Catalan number. The number n is expected to be 1 or larger.
These numbers occur in various combinatorial problems.

[list_begin arguments]
[arg_def int n] The index of the Catalan number
[list_end]

[call [cmd ::math::combinatorics::firstStirling] [arg n] [arg m]]
Calculate a Stirling number of the first kind
(signed version, m cycles in a permutation of n items)

[list_begin arguments]
[arg_def int n] Number of items
[arg_def int m] Number of cycles
[list_end]

[call [cmd ::math::combinatorics::secondStirling] [arg n] [arg m]]
Calculate a Stirling number of the second kind
(m non-empty subsets from n items)

[list_begin arguments]
[arg_def int n] Number of items
[arg_def int m] Number of subsets
[list_end]

[call [cmd ::math::combinatorics::partitionP] [arg n]]
Calculate the number of ways an integer n can be written as the sum of positive integers.

[list_begin arguments]
[arg_def int n] Number in question
[list_end]


[call [cmd ::math::combinatorics::list-permutations] [arg n]]
Return the list of permutations of the numbers 0, ..., n-1.

[list_begin arguments]
[arg_def int n] The number of items to be permuted.
[list_end]

[call [cmd ::math::combinatorics::list-variations] [arg n] [arg k]]
Return the list of variations of k numbers selected from the numbers 0, ..., n-1.
The order of the items is taken into account.

[list_begin arguments]
[arg_def int n] The number of items to be selected from.
[arg_def int k] The number of items to be selected in each variation.
[list_end]

[call [cmd ::math::combinatorics::list-combinations] [arg n] [arg k]]
Return the list of combinations of k numbers selected from the numbers 0, ..., n-1.
The order of the items is ignored.

[list_begin arguments]
[arg_def int n] The number of items to be selected from.
[arg_def int k] The number of items to be selected in each combination.
[list_end]

[call [cmd ::math::combinatorics::list-derangements] [arg n]]
Return the list of derangements of the numbers 0, ..., n-1.

[list_begin arguments]
[arg_def int n] The number of items to be rearranged.
[list_end]

[call [cmd ::math::combinatorics::list-powerset] [arg n]]
Return the list of all subsets of the numbers 0, ..., n-1.

[list_begin arguments]
[arg_def int n] The number of items to be rearranged.
[list_end]


[call [cmd ::math::combinatorics::permutationObj] new/create NAME [arg n]]
Create a TclOO object for returning permutations one by one. If the last permutation
has been reached an empty list is returned.

[list_begin arguments]
[arg_def int n] The number of items to be rearranged.
[list_end]

[call [cmd \$perm] next]
Return the next permutation of n objects.

[call [cmd \$perm] reset]
Reset the object, so that the command [term next] returns the complete list again.

[call [cmd \$perm] setElements [arg elements]]
Register a list of items to be permuted, using the [term nextElements] command.

[list_begin arguments]
[arg_def list elements] The list of n items that will be permuted.
[list_end]

[call [cmd \$perm] setElements]
Return the next permulation of the registered items.

[call [cmd ::math::combinatorics::combinationObj] new/create NAME [arg n] [arg k]]
Create a TclOO object for returning combinations one by one. If the last combination
has been reached an empty list is returned.

[list_begin arguments]
[arg_def int n] The number of items to be rearranged.
[list_end]

[call [cmd \$combin] next]
Return the next combination of n objects.

[call [cmd \$combin] reset]
Reset the object, so that the command [term next] returns the complete list again.

[call [cmd \$combin] setElements [arg elements]]
Register a list of items to be permuted, using the [term nextElements] command.

[list_begin arguments]
[arg_def list elements] The list of n items that will be permuted.
[list_end]

[call [cmd \$combin] setElements]
Return the next combination of the registered items.


[list_end]

[vset CATEGORY math]
[include ../common-text/feedback.inc]
[manpage_end]