Speaker :
 Dr. WeiHsuan Yu(University of Mariland) 
Title :

A note on spherical twodistance sets 
Time :
 20120217 (Fri) 15:30  17:00 
Place : 
Seminar Room 722, Institute of Mathematics (NTU Campus) 
Abstract: 
A spherical twodistance set is a ﬁnite collection of unit vectors in R^n such that the set of distances between any two distinct vectors has cardinality two. O.R. Musin used Delsarte’s linear programming method to prove the result when 7 ≤ n ≤ 39, except n=23. We use the semideﬁnite programming and sum of square method (SOS) to compute improved estimates of the maximum size of spherical twodistance sets. Exact answers are found for dimensions n = 23 and 40 ≤ n ≤ 94, where previous results gave divergent bounds. 