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## 第92回 2019年2月1日 14:00〜15:30

Štefan Gyürki（Univerzita Mateja Bela）「Directed strongly regular graphs」

A possible generalization of the concept of strongly regular graphs was extended to digraphs under the name directed strongly regular graphs (DSRGs). A DSRG with parameters $(n,k,t,\lambda,\mu)$ is a regular directed graph on $n$ vertices with valency $k$, such that every vertex is incident with $t$ undirected edges, and the number of paths of length 2 directed from a vertex $x$ to another vertex $y$ is $\lambda$, if there is an arc from $x$ to $y$, and $\mu$ otherwise. In the talk we present basic properties of DSRGs, several constructions and discuss possible ways for further investigations.