比利时vs摩洛哥足彩
,
university of california san diego
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math 269 - combinatorics
zhiyu wang
university of south carolina
finding berge hypergraphs by looking at the shadow
abstract:
for a fixed set of positive integers $r$, we say $\mathcal{h}$ is an $r$-uniform hypergraph, or $r$-graph, if the cardinality of each edge belongs to $r$. for a graph $g=(v,e)$, a hypergraph $\mathcal{h}$ is called a \textit{berge}-$g$, denoted by $bg$, if there is an injection $i\colon v(g)\to v(\mathcal{h})$ and a bijection $f\colon e(g) \to e(\mathcal{h})$ such that for all $e=uv \in e(g)$, we have $\{i(u), i(v)\} \subseteq f(e)$. we present some recent results about extremal problems on berge hypergraphs from the perspectives of the shadow graph. in particular, we define variants of the ramsey number and tur\'an number in berge hypergraphs, namely the \emph{cover ramsey number} and \emph{cover tur\'an number}, and show some general lower and upper bounds on these variants. we also determine the cover tur\'an density of all graphs when the uniformity of the host hypergraph equals to $3$. these results are joint work with linyuan lu.
host: ruth luo
october 29, 2019
2:00 pm
ap&m 7321
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