The Metric Nearness Problem (pdf) J. Brickell, I. Dhillon, S. Sra, J. Tropp. SIAM Journal of Matrix Analysis and Applications (SIMAX) 30(1), pp. 375-396, April 2008.
On the Existence of Equiangular Tight Frames (pdf) M. Sustik, J. Tropp, I. Dhillon, R. Jr.. Linear Algebra and its Applications 426(2), pp. 619-635, October 2007. (A previous version appears as UTCS Technical Report #TR-04-32, August 2004.)