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Coloured Loop-Erased Random Walk on the Complete Graph

Published online by Cambridge University Press:  01 November 2008

JOMY ALAPPATTU
Affiliation:
Department of Mathematics, University of California at Berkeley, 970 Evans Hall, Berkeley, CA 94720-3840, USA (e-mail: [email protected])
JIM PITMAN
Affiliation:
Department of Statistics, University of California at Berkeley, 367 Evans Hall, Berkeley, CA 94720-3860, USA (e-mail: [email protected])

Abstract

Starting from a sequence regarded as a walk through some set of values, we consider the associated loop-erased walk as a sequence of directed edges, with an edge from i to j if the loop-erased walk makes a step from i to j. We introduce a colouring of these edges by painting edges with a fixed colour as long as the walk does not loop back on itself, then switching to a new colour whenever a loop is erased, with each new colour distinct from all previous colours. The pattern of colours along the edges of the loop-erased walk then displays stretches of consecutive steps of the walk left untouched by the loop-erasure process. Assuming that the underlying sequence generating the loop-erased walk is a sequence of independent random variables, each uniform on [N] := {1, 2, . . ., N}, we condition the walk to start at N and stop the walk when it first reaches the subset [k], for some 1 ≤ kN − 1. We relate the distribution of the random length of this loop-erased walk to the distribution of the length of the first loop of the walk, via Cayley's enumerations of trees, and via Wilson's algorithm. For fixed N and k, and i = 1, 2, . . ., let Bi denote the events that the loop-erased walk from N to [k] has i + 1 or more edges, and the ith and (i + 1)th of these edges are coloured differently. We show that, given that the loop-erased random walk has j edges for some 1 ≤ jNk, the events Bi for 1 ≤ ij − 1 are independent, with the probability of Bi equal to 1/(k + i + 1). This determines the distribution of the sequence of random lengths of differently coloured segments of the loop-erased walk, and yields asymptotic descriptions of these random lengths as N → ∞.

Type
Paper
Copyright
Copyright © Cambridge University Press 2008

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References

[1]Aldous, D. J. (1991) The continuum random tree I. Ann. Probab. 19 128.CrossRefGoogle Scholar
[2]Camarri, M. and Pitman, J. (2000) Limit distributions and random trees derived from the birthday problem with unequal probabilities. Electron. J. Probab. 5 118.CrossRefGoogle Scholar
[3]Durrett, R. (1996) Probability: Theory and Examples, Duxbury.Google Scholar
[4]Evans, S., Pitman, J. and Winter, A. (2006) Rayleigh processes, real trees, and root growth with re-grafting. Probab. Theory Rel. Fields 134 81126.CrossRefGoogle Scholar
[5]Feller, W. (1966) An Introduction to Probability Theory and Its Applications, Vol. 2, Wiley.Google Scholar
[6]Lawler, G. F. (1991) Intersections of Random Walks, Birkhäuser.Google Scholar
[7]Lyons, R. and Peres, Y. (2003) Probability on Trees and Networks, Cambridge University Press. In preparation. Current version available at http://php.indiana.edu/~rdlyons/.Google Scholar
[8]Meir, A. and Moon, J. W. (1970) The distance between points in random trees. J. Combin. Theory 8 99103.CrossRefGoogle Scholar
[9]Pittel, B. Note on exact and asymptotic distributions of the parameters of the loop-erased random walk on the complete graph. In Mathematics and Computer Science II (Versailles 2002), Trends in Mathematics, Birkhäuser.CrossRefGoogle Scholar
[10]Wilson, D. B. (1996) Generating random spanning trees more quickly than the cover time. In Proc. 28th Annual ACM Symposium on the Theory of Copmputing, ACM, pp. 296303.Google Scholar
[11]Schweinsberg, J. (2008) Loop-erased random walk on finite graphs and the Rayleigh process. J. Theoret. Probab. 21 378396.CrossRefGoogle Scholar