Combination
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For other uses, see Combination (disambiguation)}}}.
In
combinatorial mathematics, a
combination is an un-ordered collection of unique elements. Given
S, the
set of all possible unique elements, a
combination is a
subset of the elements of
S. The order of the elements in a combination is not important (two lists with the same elements in different orders are considered to be the same combination). Also, the elements cannot be repeated in a combination (every element appears uniquely once). A
k-combination (or
k-subset) is a subset with
k elements. The number of
k-combinations (each of size
k) from a set
S with
n elements (size
n) is the
binomial coefficient.
A combination is a special case of a partition of a set; specifically, a partition into two sets of size k and n-k.
See also
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