Homotopy types of Hom complexes of graph homomorphisms whose codomains are cycles

Soichiro Fujii, Yuni Iwamasa, Kei Kimura, Yuta Nozaki, Akira Suzuki

Published 2024-08-09Version 1

For simple graphs $G$ and $H$, the Hom complex $\mathrm{Hom}(G,H)$ is a polyhedral complex whose vertices are the graph homomorphisms $G\to H$. It is known that $\mathrm{Hom}(G,H)$ is homotopy equivalent to a disjoint union of points and circles when both $G$ and $H$ are cycles. We generalize this known result by showing that $\mathrm{Hom}(G,H)$ is homotopy equivalent to a disjoint union of points and circles whenever $G$ is connected and $H$ is a cycle.