The Steiner Ratio Conjecture of Gilbert-Pollak May Still Be Open
We offer evidence in the disproof of the continuity of the length of minimum inner spanning trees with respect to a parameter vector having a zero component. The continuity property is the key step of the proof of the conjecture in Du and Hwang (Proc. Nat. Acad. Sci. U.S.A. 87:9464-9466, 1990; Algorithmica 7(1):121-135, 1992). Therefore the Steiner ratio conjecture proposed by Gilbert-Pollak (SIAM J. Appl. Math. 16(1):1-29, 1968) has not been proved yet. The Steiner ratio of a round sphere has been discussed in Rubinstein and Weng (J. Comb. Optim. 1:67-78, 1997) by assuming the validity of the conjecture on a Euclidean plane in Du and Hwang (Proc. Nat. Acad. Sci. U.S.A. 87:9464-9466, 1990; Algorithmica 7(1):121-135, 1992). Hence the results in Rubinstein and Weng (J. Comb. Optim. 1:67-78, 1997) have not been proved yet.
steiner ratio spanning trees gilbert-pollak conjecture steiner trees