Article
Keywords:
graphs; adjacency matrix; eigenvalues of a graph; common neighbours
Summary:
We find all connected graphs in which any two distinct vertices have exactly two common neighbors, thus solving a problem by B. Zelinka.
References:
[1] D. Cvetković, M. Doob, H. Sachs:
Spectra of Graphs. Theory and Applications. Johann A. Barth, Heidelberg, 1995.
MR 1324340
[2] R. Diestel:
Graph Theory. Second edition, Graduate Texts in Mathematics, vol. 173, Springer, New York, 2000.
MR 1743598 |
Zbl 0957.05001
[3] B. Zelinka:
Graphs in which each pair of vertices has exactly two common neighbours. Math. Bohem. 118 (1993), 163–165.
MR 1223481 |
Zbl 0777.05092