给定任意正整数t和d(≥2),记P(t,d)为在直径d的路上加上t条边后所得图的最小直径,证明了:P(6,4)=1;当d=5,6,7时有P(6,d)=2;当d=7(2k-1)+h(k≥1,1≤h≤14)时有[d/7]≤P(6,d)≤{[d/7]+2若h=7;[d/7]+1 其他;当d=5,6,7,8时有P(7,d)=2,当d=8(2k-1)+h(k≥1,1≤h≤16)时有[d/8]≤P(7,d)≤{[d/8]若h=1;d/8+2 若h=2,3,4,5,6,7,8;[d/8]+1 其他。
Given positive integers t and d (≥2), let P (t, d) denote the minimum diameter of a graph obtained by adding t extra edges to a path with diameter d. It was proved that P(6,4)= 1, P(6,d)=2 for d=5,6,7, and [d/7]≤P(6,d)≤{[d/7]+2 if h=7;[d/7]+1 otherwise,for d=(2k-1)+h,where k≥1 and 1≤h≤14.Moreover, P(7,d)=2 for d=5,6,7,8,and [d/8]≤P(7,d){=[d/8] if h=1; ≤[d/8]+2 if h=2,3,4,5,6,7,8;≤[d/8]+1 otherwise, for d=8(2k-1)+h,where k≥1 and 1≤h≤16.