Convex independence and the structure of clone-free multipartite tournaments
Author(s) -
Darren B. Parker,
Randy F. Westhoff,
Marty J. Wolf
Publication year - 2009
Publication title -
discussiones mathematicae graph theory
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.476
H-Index - 19
eISSN - 2083-5892
pISSN - 1234-3099
DOI - 10.7151/dmgt.1432
Subject(s) - mathematics , multipartite , combinatorics , regular polygon , independence (probability theory) , clone (java method) , independence number , tournament , discrete mathematics , graph , statistics , geometry , quantum , gene , physics , quantum mechanics , quantum entanglement , biochemistry , chemistry
We investigate the convex invariants associated with two-path convexity in clone-free multipartite tournaments. Specically , we explore the relationship between the Helly number, Radon number and rank of such digraphs. The main result is a structural theorem that describes the arc relationships among certain vertices associated with vertices of a given convexly independent set. We use this to prove that the Helly number, Radon number, and rank coincide in any clone-free bipartite tournament. We then study the relationship between Helly independence and Radon independence in clone-free multipartite tournaments. We show that if the rank is at least 4 or the Helly number is at least 3, then the Helly number and the Radon number are equal.
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