Homotopy types of Hom complexes of graph homomorphisms whose codomains are cycles
Abstract
For simple graphs and , the Hom complex is a polyhedral complex whose vertices are the graph homomorphisms and whose edges connect the pairs of homomorphisms which differ in a single vertex of . Hom complexes play an important role in an algebro-topological approach to the graph coloring problem. It is known that is homotopy equivalent to a disjoint union of points and circles when both and are cycles. We generalize this known result by showing that the same holds whenever is connected and is a cycle. To this end, we explicitly construct the universal cover of each connected component of and prove that it is contractible. Additionally, we provide a simple criterion to determine whether the connected component containing a given homomorphism is homotopy equivalent to a point or circle.
Cite
@article{arxiv.2408.04802,
title = {Homotopy types of Hom complexes of graph homomorphisms whose codomains are cycles},
author = {Soichiro Fujii and Yuni Iwamasa and Kei Kimura and Yuta Nozaki and Akira Suzuki},
journal= {arXiv preprint arXiv:2408.04802},
year = {2025}
}
Comments
13 pages, 5 figures