Directed Animals, Quadratic Systems and Rewriting Systems

  • Jean-François Marckert
Keywords: directed animals, Algebraic systems of matrices, rewriting systems


A directed animal is a percolation cluster in the directed site percolation model. The aim of this paper is to exhibit a strong relation between the problem of computing the generating function G of directed animals on the square lattice, counted according to the area and the perimeter, and the problem of solving a system of quadratic equations involving unknown matrices. We present some solid evidence that some infinite explicit matrices, the fixed points of a rewriting like system are the natural solutions to this system of equations: some strong evidence is given that the problem of finding G reduces to the problem of finding an eigenvector to an explicit infinite matrix.  Similar properties are shown for other combinatorial questions concerning directed animals, and for different lattices.
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