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Tropicalizing the Graph Profiles of Some Collections of Trees

Citations
Abstract
Many important problems in extremal graph theory can be stated as certifying polynomial inequalities in graph homomorphism numbers, and in particular, many ask to certify pure binomial inequalities. For a fixed collection of graphs U, the tropicalization of the graph profile of U essentially records all valid pure binomial inequalities involving graph ho- momorphism numbers for graphs in U. Building upon ideas and techniques described by Blekherman and Raymond in 2022, we compute the tropicalization of the graph profile for K1 and S2,1k -trees for 0 ≤ k ≤ m−1, that is, stars with k+1 branches, one of which is subdi- vided. We call these almost-stars. This allows pure binomial inequalities in homomorphism numbers (or densities) for these graphs to be verified through a linear program in m + 1 variables and m + 5 constraints. We give a conjecture for the f-vector of this tropicalization. We also present a conjecture for the tropicalization of the graph profile for K1, stars, and almost-stars.
Type
Dissertation (Open Access)
Date
2024-09
Publisher
License
Attribution 4.0 International
License
http://creativecommons.org/licenses/by/4.0/