# Raziskovalni matematični seminar - Arhiv

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**Datum in ura**/ Date and time: 20.12.21

**Predavalnica**/ Location: FAMNIT-MP1 & ZOOM

**Predavatelj**/ Lecturer: Đorđe Mitrović (University of Primorska).

**Naslov**/ Title: On Automorphisms of the Double cover of circulant graphs

**Vsebina**/ Abstract:

Canonical bipartite double cover of a graph $X$ is defined to be the graph $BX \coloneqq X\times K_2$. The group $\Aut X\times S_2$ naturally appears as a subgroup of $\Aut BX$. In case $\Aut BX \cong \Aut X \times S_2$, the graph $X$ is called stable. Otherwise, it is unstable. If $X$ is additionally connected, non-bipartite and distinct vertices have distinct sets of neighbors, it is called non-trivially unstable. The behavior of $\Aut(X\times Y)$, with $X$ non-bipartite and $Y$ bipartite, heavily depends on the particular case of $\Aut BX$, where we take $Y=K_2$.

Known results about stability of Cayley graphs on cyclic (and more generally, abelian) groups of odd order are discussed. Circulant graphs are Cayley graphs of cyclic groups. In his work on symmetries of unstable graphs, Steve Wilson introduced several conditions implying instability of circulants of even order, referred to as Wilson types in the literature. It has also been conjectured that these conditions can explain all instability in circulant graphs.

Corrections, both old and new, and generalizations of Wilson types are discussed. In addition to revisiting already known counterexamples to the conjecture, obtained results are used to construct new infinite families of counterexamples. It is established that every non-trivially unstable circulant of order $2p$, $p$ an odd prime, has a Wilson type. It is also established that the same holds for every non-trivially unstable circulant of valency at most $7$.

This is joint work with Ademir Hujdurović and Dave Witte Morris.

Join the Zoom Meeting Here.

See you there!

Everyone is welcome and encouraged to attend.

**Datum in ura**/ Date and time: 6.12.21

**Predavalnica**/ Location: FAMNIT-MP1 & ZOOM

**Predavatelj**/ Lecturer: Štefko Miklavič (University of Primorska, Slovenia)

**Naslov**/ Title: Distance magic graphs

**Vsebina**/ Abstract:

Let $\Gamma$ be a graph with vertex set $V$, and let $n=|V|$. A distance magic labeling of $\Gamma$ is a bijection $\ell : V \mapsto \{1,2, \ldots, n\}$ for which there exists a positive integer $r$ such that $\sum_{y \in \Gamma(x)} \ell(y) = r$ for all vertices $y \in V$, where $\Gamma(x)$ is the neighborhood of $x$. A graph is said to be distance magic if it admits a distance magic labeling. In this talk I will discuss tetravalent distance magic circulants and distance magic Hamming graphs.

** We are looking forward to meeting you at FAMNIT-MP1. **

**O**ur Math Research Seminar will also be broadcasted via Zoom.

Join the Zoom Meeting Here.

Everyone is welcome and encouraged to attend.