A 2.75-Approximation Algorithm for the Unconstrained Traveling   Tournament Problem
  A 2.75-approximation algorithm is proposed for the unconstrained traveling tournament problem, which is a variant of the traveling tournament problem. For the unconstrained traveling tournament problem, this is the first proposal of an approximation algorithm with a constant approximation ratio. In addition, the proposed algorithm yields a solution that meets both the no-repeater and mirrored constraints. Computational experiments show that the algorithm generates solutions of good quality. 
Shinji Imahori, Tomomi Matsui, Ryuhei Miyashiro
cs.DS