2019/06/13 by Aigner-Horev, Elad, Person, Yury
#Combinatorics (math.CO) #FOS: Mathematics
paper · doi:10.48550/arxiv.1906.05614
A classical result by Rado characterises the so-called partition-regular matrices A, i.e. those matrices A for which any finite colouring of the positive integers yields a monochromatic solution to the equation Ax=0. We study the \sl asymmetric random Rado problem for the (binomial) random set [n]p in which one seeks to determine the threshold for the property that any r-colouring, r ≥ 2, of the random set has a colour i ∈ [r] admitting a solution for the matrical equation Ai x = 0, where A1,…,Ar are predetermined partition-regular matrices pre-assigned to the colours involved. We prove a 1-statement for the asymmetric random Rado property. In the symmetric setting our result retrieves the 1-statement of the \sl symmetric random Rado theorem established in a combination of results by Rödl and Ruciński~\citeRR97 and by Friedgut, Rödl and Schacht~\citeFRS10. We conjecture that our 1-statement in fact unveils the threshold for the asymmetric random Rado property, yielding a counterpart to the so-called \em Kohayakawa-Kreuter conjecture concerning the threshold for the asymmetric random Ramsey problem in graphs. We deduce the aforementioned 1-statement for the asymmetric random Rado property after establishing a broader result generalising the main theorem of Friedgut, Rödl and Schacht from~\citeFRS10. The latter then serves as a combinatorial framework through which 1-statements for Ramsey-type problems in random sets and (hyper)graphs alike can be established in the asymmetric setting following a relatively short combinatorial examination of certain hypergraphs. To establish this framework we utilise a recent approach put forth by Mousset, Nenadov and Samotij~\citeMNS18 for the Kohayakawa-Kreuter conjecture.