10.10. Combinatorics

Catalan (n)

Get n'th catalan number.

See Planetmath for more information.

Combinations (k,n)

Get all combinations of k numbers from 1 to n as a vector of vectors. (See also NextCombination)

DoubleFactorial (n)

Double factorial: n(n-2)(n-4)...

See Planetmath for more information.

Factorial (n)

Factorial: n(n-1)(n-2)...

See Planetmath for more information.

FallingFactorial (n,k)

Falling factorial: (n)_k = n(n-1)...(n-(k-1))

See Planetmath for more information.

Fibbonachi (x)

Aliases: fib

Calculate nth fibbonachi number. That is the number defined recursively by Fibbonachi(n) = Fibbonachi(n-1) + Fibbonachi(n-2) and Fibbonachi(1) = Fibbonachi(2) = 1.

See Planetmath or Mathworld for more information.

GaloisMatrix (combining_rule)

Galois matrix given a linear combining rule (a_1*x_+...+a_n*x_n=x_(n+1))

HarmonicNumber (n,r)

Aliases: HarmonicH

Harmonic Number, the n'th harmonic number of order r.

Hofstadter (n)

Hofstadter's function q(n) defined by q(1)=1, q(2)=1, q(n)=q(n-q(n-1))+q(n-q(n-2))

LinearRecursiveSequence (seed_values,combining_rule,n)

Compute linear recursive sequence using galois stepping

Multinomial (v,arg...)

Calculate multinomial coefficients

NextCombination (v,n)

Get combination that would come after v in call to combinations, first combination should be [1:k]. This function is useful if you have many combinations to go through and you don't want to waste memory to store them all.

For example with Combination you would normally write a loop like:

for n in Combinations (4,6) do (
  SomeFunction (n)
);

n:=[1:4];
do (
  SomeFunction (n)
) while not IsNull(n:=NextCombination(n,6));

Pascal (i)

Get the Pascal's triangle as a matrix. This will return an i+1 by i+1 lower diagonal matrix which is the Pascal's triangle after i iterations.

See Planetmath for more information.

Permutations (k,n)

Get all permutations of k numbers from 1 to n as a vector of vectors

RisingFactorial (n,k)

Aliases: Puchhammer

(Puchhammer) Rising factorial: (n)_k = n(n+1)...(n+(k-1))

See Planetmath for more information.

Subfactorial (n)

Subfactorial: n! times sum_{k=1}^n (-1)^k/k!

Triangular (nth)

Calculate the n'th triangular number.

See Planetmath for more information.

nCr (n,r)

Aliases: Binomial

Calculate combinations (binomial coefficient)

nPr (n,r)

Calculate permutations