Department of

Mathematics


Seminar Calendar
for events the day of Tuesday, August 31, 2021.

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Tuesday, August 31, 2021

1:00 pm in Zoom,Tuesday, August 31, 2021

Maximal Independent Sets in Clique-free Graphs

Sam Spiro (University of California, San Diego)

Abstract: An independent set $I$ of a graph $G$ is said to be a maximal independent set (MIS) if it is maximal with respect to set inclusion. Nielsen proved that the maximum number of MIS's of size $k$ in an $n$-vertex graph is asymptotic to $(n/k)^k$, with the extremal construction being a disjoint union of $k$ cliques with sizes as close to $n/k$ as possible. In this talk we study how many MIS's of size $k$ an $n$-vertex graph $G$ can have if $G$ does not contain a clique $K_t$. We prove for all fixed $k$ and $t$ that there exist such graphs with $n^{\lfloor\frac{(t-2)k}{t-1}\rfloor-o(1)}$ MIS's of size $k$ by utilizing recent work of Gowers and B. Janzer on a generalization of the Ruzsa-Szemeredi problem. We prove that this bound is essentially best possible for triangle-free graphs when $k\le 4$. This is joint work with Xiaoyu He and Jiaxi Nie.

For Zoom information, please contact Sean at SEnglish (at) illinois (dot) edu.

2:00 pm in 347 Altgeld Hall,Tuesday, August 31, 2021

Semilinear equations for non-local operators: Beyond the fractional Laplacian

Zoran Vondracek (University of Zagreb)

Abstract: In this talk I will present some results on semilinear problems in general bounded open sets for non-local operators with exterior and boundary conditions. The operators are more general than the fractional Laplacian. I will also give results in case of bounded $C^{1,1}$ open sets. Joint work with I. Biocic (Biov{c}i\'c) and V.Wagner.