Covering non-uniform hypergraphs

Endre Boros, Yair Caro, Zoltán Füredi, Raphael Yuster

Research output: Contribution to journalArticle

9 Citations (Scopus)

Abstract

A subset of the vertices in a hypergraph is a cover if it intersects every edge. Let τ(H) denote the cardinality of a minimum cover in the hypergraph H, and let us denote by g(n) the maximum of τ(H) taken over all hypergraphs H with n vertices and with no two hyperedges of the same size. We show thatg(n)<1.98n(1+o(1)). A special case corresponds to an old problem of Erdos asking for the maximum number of edges in an n-vertex graph with no two cycles of the same length. Denoting this maximum by n+f(n), we can show that f(n)≤1.98n(1+o(1)). Generalizing the above, let g(n, C, k) denote the maximum of τ(H) taken over all hypergraph H with n vertices and with at most Cik edges with cardinality i for all i=1, 2, ..., n. We prove that g(n, C, k)<(Ck!+1)n(k+1)/(k+2).These results have an interesting graph-theoretic application. For a family F of graphs, let T(n, F, r) denote the maximum possible number of edges in a graph with n vertices, which contains each member of F at most r-1 times. T(n, F, 1)=T(n, F) is the classical Turán number. Using the results above, we can compute a non-trivial upper bound for T(n, F, r) for many interesting graph families.

Original languageEnglish
Pages (from-to)270-284
Number of pages15
JournalJournal of Combinatorial Theory. Series B
Volume82
Issue number2
DOIs
Publication statusPublished - Jul 1 2001

Keywords

  • Hypergraph; covering; cycles

ASJC Scopus subject areas

  • Theoretical Computer Science
  • Discrete Mathematics and Combinatorics
  • Computational Theory and Mathematics

Fingerprint Dive into the research topics of 'Covering non-uniform hypergraphs'. Together they form a unique fingerprint.

  • Cite this