2024/12/06 by Hao Chen, Chen, Hao, Yupeng Lin +5 · 1 citation
Economics, Econometrics and Finance · Computer Science · #Game Theory and Voting Systems #Polynomial and algebraic computation
paper · pdf · doi:10.48550/arxiv.2412.04972
Many fundamental problems in extremal combinatorics are equivalent to proving certain polynomial inequalities in graph homomorphism densities. In 2011, a breakthrough result by Hatami and Norine showed that it is undecidable to verify polynomial inequalities in graph homomorphism densities. Recently, Blekherman, Raymond and Wei extended this result by showing that it is also undecidable to determine the validity of polynomial inequalities in homomorphism densities for weighted graphs with edge weights taking real values. These two results resolved a question of Lovász. In this paper, we consider the problem of determining the validity of polynomial inequalities in digraph homomorphism densities for tournaments. We prove that the answer to this problem is also undecidable.