  A factor of a graph is a spanning subgraph satisfying some given conditions.
An earlier survey of factors can be traced back to the Akiyama and Kano [J.
Graph Theory, 1985, 9: 1-42] in which they described the characterization of
factors in (bipartite) graphs and digraphs, respectively. Soon after, Kouider
and Vestergaard summarized the findings related to connected factors [Graphs
Combin., 2005, 21(1): 1-26]. Plummer extended the aforementioned research by
providing a comprehensive overview of progress made in the study of graph
factors and factorization from 1985 to 2003 [Discrete Math., 2007, 7-8:
791-821]. In this paper, we aim to summarize the relevant results regarding
factors from the perspective of eigenvalues.
