给出了7z阶树的Nordhaus-Gaddum类型谱半径即图及其补图的谱半径之和的可达上界: ρ(T)+ρ(T^c)≤√n-1+n-2, 等号成立当且仅当T≌K1,n-1,其中T^c为T的补图,K1,n-1为n阶星图,同时证明了对于n阶双星图S(α,b)的Nordhaus—Gaddum类型谱半径随α的值单调上升,其中[n-1/2]≤α≤n-3.
In this paper, the sharp upper bound on the spectral radius of Nordhaus- Gaddum type at trees is given. The paper shows that ρ(T)+ρ(T^c)≤√n-1+n-2, the equality holds if and only if T≌K1,n-1.Moreover, it is proved that the spectral radius of Nordhaus-Gaddum type for double-star S (α,b) is strictly increasing in variable α, where [n-1/2]≤α≤n-3.