Uniform Spanning Tree Research Articles

Determinantal spanning forests on planar graphs

We generalize the uniform spanning tree to construct a family of determinantal measures on essential spanning forests on periodic planar graphs in which every component tree is bi-infinite. Like the uniform spanning tree, these measures arise naturally from the Laplacian on the graph. More generally, these results hold for the “massive” Laplacian determinant which counts rooted spanning forests with weight $M$ per finite component. These measures typically have a form of conformal invariance, unlike the usual rooted spanning tree measure. We show that the spectral curve for these models is always a simple Harnack curve; this fact controls the decay of edge-edge correlations in these models. We construct a limit shape theory in these settings, where the limit shapes are defined by measured foliations of fixed isotopy type.

Speeding up non-Markovian first-passage percolation with a few extra edges

Abstract One model of real-life spreading processes is that of first-passage percolation (also called the SI model) on random graphs. Social interactions often follow bursty patterns, which are usually modelled with independent and identically distributed heavy-tailed passage times on edges. On the other hand, random graphs are often locally tree-like, and spreading on trees with leaves might be very slow due to bottleneck edges with huge passage times. Here we consider the SI model with passage times following a power-law distribution ℙ(ξ>t)∼t-α with infinite mean. For any finite connected graph G with a root s, we find the largest number of vertices κ(G,s) that are infected in finite expected time, and prove that for every k≤κ(G,s), the expected time to infect k vertices is at most O(k1/α). Then we show that adding a single edge from s to a random vertex in a random tree 𝒯 typically increases κ(𝒯,s) from a bounded variable to a fraction of the size of 𝒯, thus severely accelerating the process. We examine this acceleration effect on some natural models of random graphs: critical Galton--Watson trees conditioned to be large, uniform spanning trees of the complete graph, and on the largest cluster of near-critical Erdős‒Rényi graphs. In particular, at the upper end of the critical window, the process is already much faster than exactly at criticality.

Random Forests and Networks Analysis

Wilson (Proceedings of the twenty-eight annual acm symposium on the theory of computing, pp. 296–303, 1996) in the 1990s described a simple and efficient algorithm based on loop-erased random walks to sample uniform spanning trees and more generally weighted trees or forests spanning a given graph. This algorithm provides a powerful tool in analyzing structures on networks and along this line of thinking, in recent works (Avena and Gaudillière in A proof of the transfer-current theorem in absence of reversibility, in Stat. Probab. Lett. 142, 17–22 (2018); Avena and Gaudillière in J Theor Probab, 2017. https://doi.org/10.1007/s10959-017-0771-3; Avena et al. in Approximate and exact solutions of intertwining equations though random spanning forests, 2017. arXiv:1702.05992v1; Avena et al. in Intertwining wavelets or multiresolution analysis on graphs through random forests, 2017. arXiv:1707.04616, to appear in ACHA (2018)) we focused on applications of spanning rooted forests on finite graphs. The resulting main conclusions are reviewed in this paper by collecting related theorems, algorithms, heuristics and numerical experiments. A first foundational part on determinantal structures and efficient sampling procedures is followed by four main applications: (1) a random-walk-based notion of well-distributed points in a graph, (2) a framework to describe metastable-like dynamics in finite settings by means of Markov intertwining dualities, (3) coarse graining schemes for networks and associated processes, (4) wavelets-like pyramidal algorithms for graph signals.

A proof of the transfer-current theorem in absence of reversibility

The transfer-current theorem is a well-known result in probability theory stating that edges in a uniform spanning tree of an undirected graph form a determinantal process with kernel interpretable in terms of flows. Its original derivation due to Burton and Pemantle (1993) is based on a clever induction using comparison of random walks with electrical networks. Several variants of this celebrated result have recently appeared in the literature. In this paper we give an elementary proof of an extension of this theorem when the underlying graph is directed, irreducible and finite. Further, we give a characterization of the corresponding determinantal kernel in terms of flows extending the kernel given by Burton–Pemantle to the non-reversible setting.

Cohen–Lenstra Heuristics for Torsion in Homology of Random Complexes

ABSTRACTWe study torsion in homology of the random d-complex Y ∼ Yd(n, p) experimentally. Our experiments suggest that there is almost always a moment in the process, where there is an enormous burst of torsion in homology Hd − 1(Y). This moment seems to coincide with the phase transition studied in [Aronshtam and Linial 13, Linial and Peled 16, Linial and Peled 17], where cycles in Hd(Y) first appear with high probability.Our main study is the limiting distribution on the q-part of the torsion subgroup of Hd − 1(Y) for small primes q. We find strong evidence for a limiting Cohen–Lenstra distribution, where the probability that the q-part is isomorphic to a given q-group H is inversely proportional to the order of the automorphism group |Aut(H)|.We also study the torsion in homology of the uniform random -acyclic 2-complex. This model is analogous to a uniform spanning tree on a complete graph, but more complicated topologically since Kalai showed that the expected order of the torsion group is exponentially large in n2 [Kalai 83]. We give experimental evidence that in this model also, the torsion is Cohen–Lenstra distributed in the limit.

Local limits of lozenge tilings are stable under bounded boundary height perturbations

We show that bounded changes to the boundary of a lozenge tilings do not affect the local behaviour inside the domain. As a consequence we prove the existence of a local limit in all domains with planar boundary. The proof does not rely on any exact solvability of the model beyond its links with uniform spanning trees.

SLE as a Mating of Trees in Euclidean Geometry

The mating of trees approach to Schramm-Loewner evolution (SLE) in the random geometry of Liouville quantum gravity (LQG) has been recently developed by Duplantier-Miller-Sheffield (2014). In this paper we consider the mating of trees approach to SLE in Euclidean geometry. Let $\eta$ be a whole-plane space-filling SLE with parameter $\kappa>4$, parameterized by Lebesgue measure. The main observable in the mating of trees approach is the contour function, a two-dimensional continuous process describing the evolution of the Minkowski content of the left and right frontier of $\eta$. We prove regularity properties of the contour function and show that (as in the LQG case) it encodes all the information about the curve $\eta$. We also prove that the uniform spanning tree on $\mathbb Z^2$ converges to $\mathrm{SLE}_8$ in the natural topology associated with the mating of trees approach.

The Local Limit of the Uniform Spanning Tree on Dense Graphs

Let $G$ be a connected graph in which almost all vertices have linear degrees and let $T$ be a uniform spanning tree of $G$. For any fixed rooted tree $F$ of height $r$ we compute the asymptotic density of vertices $v$ for which the $r$-ball around $v$ in $T$ is isomorphic to $F$. We deduce from this that if $\{G_n\}$ is a sequence of such graphs converging to a graphon $W$, then the uniform spanning tree of $G_n$ locally converges to a multi-type branching process defined in terms of $W$. As an application, we prove that in a graph with linear minimum degree, with high probability, the density of leaves in a uniform spanning tree is at least $1/e-o(1)$, the density of vertices of degree $2$ is at most $1/e+o(1)$ and the density of vertices of degree $k\geq 3$ is at most ${(k-2)^{k-2} \over (k-1)! e^{k-2}} + o(1)$. These bounds are sharp.

Subsequential scaling limits of simple random walk on the two-dimensional uniform spanning tree

The first main result of this paper is that the law of the (rescaled) two-dimensional uniform spanning tree is tight in a space whose elements are measured, rooted real trees continuously embedded into Euclidean space. Various properties of the intrinsic metrics, measures and embeddings of the subsequential limits in this space are obtained, with it being proved in particular that the Hausdorff dimension of any limit in its intrinsic metric is almost surely equal to $8/5$. In addition, the tightness result is applied to deduce that the annealed law of the simple random walk on the two-dimensional uniform spanning tree is tight under a suitable rescaling. For the limiting processes, which are diffusions on random real trees embedded into Euclidean space, detailed transition density estimates are derived.

Fundamental constants in the theory of two-dimensional uniform spanning trees

Three characteristics of two-dimensional uniform spanning trees are nontrivially related to one another: the average density of a sandpile, the looping constant of a square lattice, and the return probability of a loop-erased random walk. We briefly trace the long history of the discovery of their unexpected rational values.

Fundamental constants in the theory of two-dimensional uniform spanning trees

Три характеристики двумерных покрывающих деревьев связаны между собой нетривиальными соотношениями: средняя высота в модели "песочной горки", петлевая константа квадратной решетки и вероятность возврата случайного блуждания со стертыми петлями. Кратко прослежена долгая история вывода их неожиданных рациональных значений.

Pfaffian Formulas for Spanning Tree Probabilities

We show that certain topologically defined uniform spanning tree probabilities for graphs embedded in an annulus can be computed as linear combinations of Pfaffians of matrices involving the line-bundle Green's function, where the coefficients count cover-inclusive Dyck tilings of skew Young diagrams.

UNIFORM SPANNING TREES ON SIERPI NSKI GRAPHS

We study spanning trees on Sierpi nski graphs (i.e., nite approxima- tions to the Sierpi nski gasket) that are chosen uniformly at random. We prove existence of a limit measure and derive a number of structural results, for instance on the degree distribution. The connection between uniform spanning trees and loop-erased random walk is then exploited to prove convergence of the latter to a continuous stochastic process akin to the Brownian motion or the Schramm- Loewner evolution. Some geometric properties of this limit process, such as the Hausdor dimension, are investigated as well. The method is also applicable to other self-similar graphs with a sucient degree of symmetry.

Concentration of Lipschitz Functionals of Determinantal and Other Strong Rayleigh Measures

Let {X1 , . . , Xn} be a collection of binary-valued random variables and let f : {0, 1}n → $\mathbb{R}$ be a Lipschitz function. Under a negative dependence hypothesis known as the strong Rayleigh condition, we show that f − ${\mathbb E}$f satisfies a concentration inequality. The class of strong Rayleigh measures includes determinantal measures, weighted uniform matroids and exclusion measures; some familiar examples from these classes are generalized negative binomials and spanning tree measures. For instance, any Lipschitz-1 function of the edges of a uniform spanning tree on vertex set V (e.g., the number of leaves) satisfies the Gaussian concentration inequality \begin{linenomath}$${{\mathbb P} (f - {\mathbb E} f \geq a) \leq \exp \biggl( - \frac{a^2}{8 \, |V|} \biggr) }.$$\end{linenomath} We also prove a continuous version for concentration of Lipschitz functionals of a determinantal point process.

Loop-erased random walk on the Sierpinski gasket

In this paper the loop-erased random walk on the finite pre-Sierpiński gasket is studied. It is proved that the scaling limit exists and is a continuous process. It is also shown that the path of the limiting process is almost surely self-avoiding, while having Hausdorff dimension strictly greater than 1. The loop-erasing procedure proposed in this paper is formulated by erasing loops, in a sense, in descending order of size. It enables us to obtain exact recursion relations, making direct use of ‘self-similarity’ of a fractal structure, instead of the relation to the uniform spanning tree. This procedure is proved to be equivalent to the standard procedure of chronological loop-erasure.

Spectral Dimension and Random Walks on the Two Dimensional Uniform Spanning Tree

We study the simple random walk on the uniform spanning tree on $${\mathbb {Z}^2}$$ . We obtain estimates for the transition probabilities of the random walk, the distance of the walk from its starting point after n steps, and exit times of both Euclidean balls and balls in the intrinsic graph metric. In particular, we prove that the spectral dimension of the uniform spanning tree on $${\mathbb {Z}^2}$$ is 16/13 almost surely.

Probability on graphs: random processes on graphs and lattices

Preface 1. Random walks on graphs 2. Uniform spanning tree 3. Percolation and self-avoiding walk 4. Association and influence 5. Further percolation 6. Contact process 7. Gibbs states 8. Random-cluster model 9. Quantum Ising model 10. Interacting particle systems 11. Random graphs 12. Lorentz gas References Index.

Dimension of the loop-erased random walk in three dimensions

We measure the fractal dimension of loop-erased random walk (LERW) in three dimensions and estimate that it is 1.624 00 ± 0.000 05. LERW is closely related to the uniform spanning tree and the Abelian sandpile model. We simulated LERW on both the cubic and face-centered-cubic lattices; the corrections to scaling are slightly smaller for the face-centered-cubic lattice.

Resolvent of large random graphs

AbstractWe analyze the convergence of the spectrum of large random graphs to the spectrum of a limit infinite graph. We apply these results to graphs converging locally to trees and derive a new formula for the Stieltjes transform of the spectral measure of such graphs. We illustrate our results on the uniform regular graphs, Erdös‐Rényi graphs and graphs with a given degree sequence. We give examples of application for weighted graphs, bipartite graphs and the uniform spanning tree of n vertices. © 2010 Wiley Periodicals, Inc. Random Struct. Alg., 2010

The dimension of the SLE curves

Let γ be the curve generating a Schramm–Loewner Evolution (SLE) process, with parameter κ ≥ 0. We prove that, with probability one, the Haus-dorff dimension of γ is equal to Min(2, 1 + κ/8). Introduction. It has been conjectured by theoretical physicists that various lattice models in statistical physics (such as percolation, Potts model, Ising model, uniform spanning trees), taken at their critical point, have a continuous confor-mally invariant scaling limit when the mesh of the lattice tends to 0. Recently, Oded Schramm [15] introduced a family of random processes which he called Stochastic Loewner Evolutions (or SLE), that are the only possible conformally invariant scaling limits of random cluster interfaces (which are very closely related to all above-mentioned models). An SLE process is defined using the usual Loewner equation, where the driving function is a time-changed Brownian motion. More specifically, in the present paper we will be mainly concerned with SLE in the upper-half plane (sometimes called chordal SLE), defined by the following PDE: