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For any pair of positive integers n and k, the number of k-tuples of positive integers whose sum is n is equal to the number of (k − 1)-element subsets of a set with n − 1 elements. For example, if n = 10 and k = 4, the theorem gives the number of solutions to x 1 + x 2 + x 3 + x 4 = 10 (with x 1, x 2, x 3, x 4 > 0) as the binomial coefficient
By formulating MAX-2-SAT as a problem of finding a cut (that is, a partition of the vertices into two subsets) maximizing the number of edges that have one endpoint in the first subset and one endpoint in the second, in a graph related to the implication graph, and applying semidefinite programming methods to this cut problem, it is possible to ...
A Langford pairing for n = 4.. In combinatorial mathematics, a Langford pairing, also called a Langford sequence, is a permutation of the sequence of 2n numbers 1, 1, 2, 2, ..., n, n in which the two 1s are one unit apart, the two 2s are two units apart, and more generally the two copies of each number k are k units apart.
To find it, start at such a p 0 containing at least two individuals in their reduced list, and define recursively q i+1 to be the second on p i 's list and p i+1 to be the last on q i+1 's list, until this sequence repeats some p j, at which point a rotation is found: it is the sequence of pairs starting at the first occurrence of (p j, q j ...
An example of a counting problem whose solution can be given in terms of the Narayana numbers (,), is the number of words containing pairs of parentheses, which are correctly matched (known as Dyck words) and which contain distinct nestings.
In a uniformly-random instance of the stable marriage problem with n men and n women, the average number of stable matchings is asymptotically . [6] In a stable marriage instance chosen to maximize the number of different stable matchings, this number is an exponential function of n . [ 7 ]
In it, a subset of edges is independent if its removal does not separate the graph. Any spanning tree of the original graph that avoids the edges used in the matroid parity solution is necessarily a Xuong tree. Each pair selected in the solution can be used to increase the genus of the embedding, so the total genus is the number of selected ...
Take for example the group of pairs, adding each component separately modulo some . By omitting one of the components, we suddenly find ourselves in Z n {\displaystyle \mathbb {Z} _{n}} (and this mapping is obviously compatible with the respective additions, i.e. it is a group homomorphism ).