Edge-extremal graphs under degree and matching number restrictions.

Edge-extremal graphs under degree and matching number restrictions.

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Tınaz Ekim, Boğaziçi University
Fine Hall 224

We determine the maximum number of edges that a claw-free graph can have, when its maximum degree and matching number are bounded. This is a famous problem that has been studied on general graphs, and for which there is a tight bound. The graphs achieving this bound contain in most cases an induced copy of a claw, which motivates studying the question on claw-free graphs. Note that on general graphs, if one of the mentioned parameters is not bounded, then there is no upper bound on the number of edges. We show that on claw-free graphs, bounding the matching number is sufficient for obtaining an upper bound on the number of edges. The same is not true for the degree, as a long path is claw-free. We give exact tight formulas for both when only the matching number is bounded and when both parameters are bounded. We also construct claw-free graphs whose edge numbers match the given bounds. We conclude with several open questions that could be interesting to investigate further. Joint with Cemil Dibek and Pinar Heggernes.