摘要
Lin-Lu-Yau introduced a notion of Ricci curvature for graphs and obtained a complete classification for all Ricci-flat graphs with girth at least five.In this paper,we characterize all Ricci-flat graphs of girth four with vertex-disjoint 4-cycles.
基金
Supported by the National Natural Science Foundation of China(Grant Nos.11601093,12025109,12071489 and 61976104)
the Research Fund of Guangdong University of Foreign Studies(Grant Nos.299-X5219228 and 297-ZW200011)。
