Self-avoiding walks contained within a square

TL;DR

This paper investigates the asymptotic behavior of self-avoiding walks within a square, providing numerical enumeration data, conjecturing growth formulas, and analyzing related polygon cycles.

Contribution

It introduces a detailed numerical analysis and conjectured asymptotic formulas for self-avoiding walks and polygons in a square, including special subsets and boundary conditions.

Findings

Growth constant λ ≈ 1.74455 for walks and polygons.

Walks with boundary contact grow at the same rate as crossing walks.

Polygons exhibit similar growth with different parameters, notably g ≈ -0.5.

Abstract

We have studied self-avoiding walks contained within an $L \times L$ square whose end-points can lie anywhere within, or on, the boundaries of the square. We prove that such walks behave, asymptotically, as walks crossing a square (WCAS), being those walks whose end-points lie at the south-east and north-west corners of the square. We provide numerical data, enumerating all such walks, and analyse the sequence of coefficients in order to estimate the asymptotic behaviour. We also studied a subset of these walks, those that must contain at least one edge on all four boundaries of the square. We provide compelling evidence that these two classes of walks grow identically. From our analysis we conjecture that the number of such walks $C_L$, for both problems, behaves as $$ C_L \sim \lambda^{L^2+bL+c}\cdot L^g,$$ where $\lambda= 1.7445498 \pm 0.0000012,$ $b=-0.04354 \pm 0.0005,$ $c=-1.35 \pm 0.45,$ and $g=3.9 \pm 0.1.$ Finally, we also studied the equivalent problem for self-avoiding polygons, also known as cycles in a square grid. The asymptotic behaviour of cycles has the same form as walks, but with different values of the parameters $c$, and $g$. Our numerical analysis shows that $\lambda$ and $b$ have the same values as for WCAS and that $c=1.776 \pm 0.002$ while $g=-0.500\pm 0.005$ and hence probably equals $-\frac12$.