Alternating sign matrix
In mathematics, an alternating sign matrix is a square matrix of 0s, 1s, and −1s such that the sum of each row and column is 1 and the nonzero entries in each row and column alternate in sign. These matrices generalize permutation matrices and arise naturally when using Dodgson condensation to compute a determinant. They are also closely related to the six-vertex model with domain wall boundary conditions from statistical mechanics. They were first defined by William Mills, David Robbins, and Howard Rumsey in the former context.
An example of an alternating sign matrix (that is not also a permutation matrix) is
Alternating sign matrix conjecture
The alternating sign matrix conjecture states that the number of alternating sign matrices is
The first few terms in this sequence for n = 0, 1, 2, 3, … are
This conjecture was first proved by Doron Zeilberger in 1992. In 1995, Greg Kuperberg gave a short proof based on the Yang-Baxter equation for the six vertex model with domain wall boundary conditions, that uses a determinant calculation, which solves recurrence relations due to Vladimir Korepin.
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