图与其补图特征值之和的界
Bounds on the Sum of the Eigenvalues of a Graph and Its Complement
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摘要: 设G是n阶简单图,其补图记为G^c,λi(G)为G的第i大特征值。文中给出了图与其补图几个常见的特征值之和的界(i=1,2,…,n):-√2(n-1)(i-1)/(n-i+1)≤λi(G)+λi(G^c)≤√2(n-i)(n-1)/i (Ⅰ) 及 (n-1)≤λi(G)+λ1(G^c)≤-1+√1+2n(n-1) (Ⅱ) (Ⅱ)式中,下界可达当且仅当G为正则图。