
Revised: May 18, 2014
Published: June 18, 2015
Abstract: [Plain Text Version]
We show improved NP-hardness of approximating Ordering-Constraint Satisfaction Problems (OCSPs). For the two most well-studied OCSPs, Maximum Acyclic Subgraph and Maximum Betweenness, we prove NP-hard approximation factors of 14/15+ε and 1/2+ε. When it is hard to approximate an OCSP by a constant better than taking a uniformly-at-random ordering, then the OCSP is said to be approximation resistant. We show that the Maximum Non-Betweenness Problem is approximation resistant and that there are width-m approximation-resistant OCSPs accepting only a fraction 1/(m/2)! of assignments. These results provide the first examples of approximation-resistant OCSPs subject only to P≠NP.
An extended abstract of this paper appeared in the 15th International Workshop on Approximation Algorithms for Combinatorial Optimization Problems (APPROX 2013).