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A positivity phenomenon in Elser's Gaussian-cluster percolation model
Dorpalen-Barry, Galen Hettle, Cyrus Livingston, David C. Martin, Jeremy L. Nasr, George D. Vega, Julianne Whitlatch, Hays
Dorpalen-Barry, Galen
Hettle, Cyrus
Livingston, David C.
Martin, Jeremy L.
Nasr, George D.
Vega, Julianne
Whitlatch, Hays
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Abstract
Veit Elser proposed a random graph model for percolation in which physical dimension appears as a parameter. Studying this model combinatorially leads naturally to the consideration of numerical graph invariants which we call Elser numbers els_k(G), where G is a connected graph and k a nonnegative integer. Elser had proven that els_1(G) = 0 for all G. By interpreting the Elser numbers as reduced Euler characteristics of appropriate simplicial complexes called nucleus complexes, we prove that for all graphs G, they are nonpositive when k = 0 and nonnegative for k ≥ 2. The last result confirms a conjecture of Elser. Furthermore, we give necessary and sufficient conditions, in terms of the 2-connected structure of G, for the nonvanishing of the Elser numbers.
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Date
2020-12-18
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Elsevier
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Keywords
Graph, Simplicial complex, Euler characteristic, Nucleus, Percolation, Block-cutpoint tree
Citation
Galen Dorpalen-Barry, Cyrus Hettle, David C. Livingston, Jeremy L. Martin, George D. Nasr, Julianne Vega, Hays Whitlatch, "A positivity phenomenon in Elser's Gaussian-cluster percolation model", Journal of Combinatorial Theory, Series A, Volume 179, 2021, 105364,
ISSN 0097-3165, https://doi.org/10.1016/j.jcta.2020.105364.