arXiv subjects

Yury Person

Publications and source records attributed to Yury Person.

41 records · Page 3Linked to original sources

arXiv2013

On the rank of higher inclusion matrices

Let r >= s >= 0 be integers and G be an r-graph. The higher inclusion matrix M_s^r(G) is a {0,1}-matrix with rows indexed by the edges of G and columns indexed by the subsets of V(G) of size s: the entry corresponding to an edge e and a subset S is 1 if S is contained in e and 0 otherwise. Following a question of Frankl and Tokushige and a result of Keevash, we define the rank-extremal function rex(n,t,r,s) as the maximum number of edges of an r-graph G having rank M_s^r(G) <=\binom{n}{s} - t. For t at most linear in n we determine this function as well as the extremal r-graphs. The special case t=1 answers a question of Keevash.

math.CO↗

arXiv2013

Tight Hamilton cycles in random hypergraphs

We give an algorithmic proof for the existence of tight Hamilton cycles in a random r-uniform hypergraph with edge probability p=n^{-1+eps} for every eps>0. This partly answers a question of Dudek and Frieze [Random Structures Algorithms], who used a second moment method to show that tight Hamilton cycles exist even for p=omega(n)/n (r>2) where omega(n) tends to infinity arbitrary slowly, and for p=(e+o(1))/n (r>3). The method we develop for proving our result applies to related problems as well.

math.CO↗

arXiv2012

A regularity lemma and twins in words

For a word $S$, let $f(S)$ be the largest integer $m$ such that there are two disjoints identical (scattered) subwords of length $m$. Let $f(n, Σ) = \min \{f(S): S \text{is of length} n, \text{over alphabet} Σ\}$. Here, it is shown that \[2f(n, \{0,1\}) = n-o(n)\] using the regularity lemma for words. I.e., any binary word of length $n$ can be split into two identical subwords (referred to as twins) and, perhaps, a remaining subword of length $o(n)$. A similar result is proven for $k$ identical subwords of a word over an alphabet with at most $k$ letters.

math.CO↗

arXiv2011

On extremal hypergraphs for hamiltonian cycles

We study sufficient conditions for Hamiltonian cycles in hypergraphs, and obtain both Turán- and Dirac-type results. While the Turán-type result gives an exact threshold for the appearance of a Hamiltonian cycle in a hypergraph depending only on the extremal number of a certain path, the Dirac-type result yields a sufficient condition relying solely on the minimum vertex degree.

math.CO↗

arXiv2011

An improved error term for minimum H-decompositions of graphs

We consider partitions of the edge set of a graph G into copies of a fixed graph H and single edges. Let ϕ_H(n) denote the minimum number p such that any n-vertex G admits such a partition with at most p parts. We show that ϕ_H(n)=ex(n,K_r)+Θ(biex(n,H)) for χ(H)>2, where biex(n,H) is the extremal number of the decomposition family of H. Since biex(n,H)=O(n^{2-γ}) for some γ>0 this improves on the bound ϕ_H(n)=ex(n,H)+o(n^2) by Pikhurko and Sousa [J. Combin. Theory Ser. B 97 (2007), 1041-1055]. In addition it extends a result of Özkahya and Person [J. Combin. Theory Ser. B, to appear].

math.CO↗