The concepts of critical and cocritical radius edge-invariant graphs are introduced. We prove that every graph can be embedded as an induced subgraph of a critical or cocritical radius-edge-invariant graph. We show that every cocritical radius-edge-invariant graph of radius r ≥ 15 must have at least 3r+2 vertices.
Department of Mathematics and Descriptive Geometry, Faculty of Wood Sciences and Technology, Technical University Zvolen, T.G. Masaryka 24, 960 53 Zvolen, Slovak Republic
Bibliografia
[1] V. Bálint and O. Vacek, Radius-invariant graphs, Math. Bohem. 129 (2004) 361-377.
[2] F. Buckley and F. Harary, Distance in Graphs (Addison-Wesley, Redwood City, 1990).
[3] R.D. Dutton, S.R. Medidi and R.C. Brigham, Changing and unchanging of the radius of graph, Linear Algebra Appl. 217 (1995) 67-82, doi: 10.1016/0024-3795(94)00153-5.
[4] F. Gliviak, On radially extremal graphs and digraphs, a survey, Math. Bohem. 125 (2000) 215-225.