Improving Implementation of SAT Competitions 2017–2019 Winners

Abstract

The results of annual SAT competitions are often viewed as the milestones showcasing the progress in SAT solvers. However, their competitive nature leads to the situation when the majority of this year's solvers are based on previous year's winner. And since the main focus is always on novelty, it means that there are times when some implementation details have a potential for improvement, but they are just inherited from solver to solver for several years in a row. In this study we propose small modifications of implementations of existing heuristics in several related SAT solvers. These modifications mostly consist in employing a deterministic strategy for switching between branching heuristics and in augmentations of the treatment of Tier2 and Core clauses. In our experiments we show that the proposed changes have a positive effect on solvers' performance both individually and in combination with each other.

Boosting the Performance of CDCL-Based SAT Solvers by Exploiting Backbones and Backdoors

“…Therefore, improvements in VSIDS have led to improved performance for both variants in solving more satisfiable instances. It is therefore evident that VSIDS is not only superior at solving unsatisfiable instances [51] but could even be improved to solve satisfiable instances as well.…”

“…VSIDS refers to a class of branching heuristics commonly used in CDCL SAT solvers that rank all the variables in an SAT instance during the run of the solver. VSIDS is significantly more effective than other well-known heuristics, particularly when solving unsatisfiable SAT instances [51,54,55]. The VSIDS heuristic was originally proposed as part of the Chaff solver [6].…”