Bootstrap Percolation in High Dimensions

Combinatorics Probability and Computing - Tập 19 Số 5-6 - Trang 643-692 - 2010
József Balogh1, Béla Bollobás2, Robert Morris3
1Department of mathematics, university of illinois, 1409 w. green street, urbana, il 61801 and department of mathematics, university of california, san diego, la jolla, ca 92093 (e-mail: [email protected] ...#TAB#
2Trinity college, cambridge cb2 1tq, england and department of mathematical sciences, the university of memphis, memphis, tn 38152, usa (e-mail: [email protected])#TAB#
3Impa, estrada dona castorina 110, jardim botânico, rio de janeiro, rj, brasil (e-mail: [email protected])#TAB#

Tóm tắt

Inr-neighbour bootstrap percolation on a graphG, a set of initially infected verticesAV(G) is chosen independently at random, with densityp, and new vertices are subsequently infected if they have at leastrinfected neighbours. The setAis said to percolate if eventually all vertices are infected. Our aim is to understand this process on the grid, [n]d, for arbitrary functionsn=n(t),d=d(t) andr=r(t), ast→ ∞. The main question is to determine the critical probabilitypc([n]d,r) at which percolation becomes likely, and to give bounds on the size of the critical window. In this paper we study this problem whenr= 2, for all functionsnanddsatisfyingd≫ logn.The bootstrap process has been extensively studied on [n]dwhendis a fixed constant and 2 ⩽rd, and in these casespc([n]d,r) has recently been determined up to a factor of 1 +o(1) asn→ ∞. At the other end of the scale, Balogh and Bollobás determinedpc([2]d, 2) up to a constant factor, and Balogh, Bollobás and Morris determinedpc([n]d,d) asymptotically ifd≥ (log logn)2+ϵ, and gave much sharper bounds for the hypercube.Here we prove the following result. Let λ be the smallest positive root of the equationso λ ≈ 1.166. Thenifdis sufficiently large, and moreoverasd→ ∞, for every functionn=n(d) withd≫ logn.

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