Bart Litjens

activity

20162019

collaborators

8 papers

math.CO2019

Tutte's dichromate for signed graphs

Andrew Goodall, Bart Litjens, Guus Regts +1

We introduce the ``trivariate Tutte polynomial" of a signed graph as an invariant of signed graphs up to vertex switching that contains among its evaluations the number of proper c…

math.CO2018

A Tutte polynomial for maps II: the non-orientable case

Andrew Goodall, Bart Litjens, Guus Regts +1

We construct a new polynomial invariant of maps (graphs embedded in a compact surface, orientable or non-orientable), which contains as specializations the Krushkal polynomial, the…

math.CO2018

On the circular chromatic number of a subgraph of the Kneser graph

Bart Litjens, Sven Polak, Bart Sevenster +1

Let $n, k, r$ be positive integers with $n \geq r k$ and $r \geq 2$ . Consider a circle $C$ with~ $n$ points~ $1, \dots, n$ in clockwise order. The $r$ -stable \emph{interlacing graph} $\t…

math.CO2017

Sum-perfect graphs

Bart Litjens, Sven Polak, Vaidy Sivaraman

Inspired by a famous characterization of perfect graphs due to Lovász, we define a graph $G$ to be sum-perfect if for every induced subgraph $H$ of $G$ , $α (H) + ω (H) \geq ∣ V (H) ∣$ .…

math.CO2017

On dihedral flows in embedded graphs

Bart Litjens

Let $Γ$ be a multigraph with for each vertex a cyclic order of the edges incident with it. For $n \geq 3$ , let $D_{2 n}$ be the dihedral group of order $2 n$ . Define $\mathbb{D} := \…

math.CO2017

Partition functions and a generalized coloring-flow duality for embedded graphs

Bart Litjens, Bart Sevenster

Let $G$ be a finite group and $χ : G \to C$ a class function. Let $H = (V, E)$ be a directed graph with for each vertex a cyclic order of the edges incident to it. T…