Ordinary and Spectral Extremal Problems on Vertex Disjoint Copies of Even Fans
摘要
Let ex(n, F) and spex(n, F) be the maximum size and spectral radius among all F-free graphs with fixed order n, respectively. A fan is a graph P1 ∨ Ps (join of a vertex and a path of order s) for s ≥ 3, and it is called an even fan if s is even. In this paper, we study ex(n, t(P1 ∨ P2k)), spex(n, t(P1 ∨ P2k)) with t ≥ 1 and k ≥ 3 and characterize the corresponding extremal graphs for sufficiently large n.