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Vertex colouring, Edge Colouring, List Colouring, Fractional Chromatic Number and other variants of graph colouring problems are all on topic.

6 votes
1 answer
595 views

Combinatorial equation system with exponentially many equations in quadratic many variables

A certain question on graph theory (about the existance of graphs with a certain coloring inherited by perfect matchings) can be translated into the satisfiability problem of a certain set of equation …
Mario Krenn's user avatar
21 votes
1 answer
1k views

Smallest known counterexamples to Hedetniemi’s conjecture

In 2019, Shitov has shown a counterexample (Ann. Math, 190(2) (2019) pp. 663-667) to Hedetniemi’s conjecture, $$\chi(G \times H)=\min(\chi(G),\chi(H))$$ where $\chi(G)$ is the chromatic number of the …
Mario Krenn's user avatar
10 votes
0 answers
741 views

Has this notion of vertex-coloring of graphs been studied?

In a study of a quantum physics problem, I came about an apparently very natural type of vertex colorings of a graph. The colors of the vertex $v_i$ is inherited from perfect matchings $PM$ of an edge …
Mario Krenn's user avatar
11 votes
1 answer
816 views

Graphs with only disjoint perfect matchings, with coloring

The following purely graph-theoretic question is motivated by quantum mechanics. Definitions: A bi-colored graph $G$ is an undirected graph where every edge is colored. An edge can either be monochro …
Mario Krenn's user avatar
32 votes
0 answers
3k views

Vertex coloring inherited from perfect matchings (motivated by quantum physics)

Added (19.01.2021): Dustin Mixon wrote a blog post about the question where he reformulated and generalized the question. Added (25.12.2020): I made a youtube video to explain the question in detail. …
Mario Krenn's user avatar