Assuming VSIDS's computational cost is negligible, we can compute the wall clock time of MiniSat Figure 6 confirms that the dependence is linear. We call the middle part'the core'. The output of the core is concatenated with the output of the encoder and gets fed to the core again. We describe all the hyperparameters in Appendix C.3. Encoder and Decoder are independent graph networks, i.e.

The two most effective branching strategies LRB and VSIDS perform differently on different types of instances. Generally, LRB is more effective on crafted instances, while VSIDS is more effective on application ones. However, distinguishing the types of instances is difficult. To overcome this drawback, we propose a branching strategy selection approach based on the vivification ratio. This approach uses the LRB branching strategy more to solve the instances with a very low vivification ratio. We tested the instances from the main track of SAT competitions in recent years. The results show that the proposed approach is robust and it significantly increases the number of solved instances. It is worth mentioning that, with the help of our approach, the solver Maple\_CM can solve more than 16 instances for the benchmark from the 2020 SAT competition.

A BSTRACT We present GQSA T, a branching heuristic in a Boolean SA T solver trained with value-based reinforcement learning (RL) using Graph Neural Networks for function approximation. Solvers using GQSA T are complete SA T solvers that either provide a satisfying assignment or a proof of unsatisfiability, which is required for many SA T applications. The branching heuristic commonly used in SA T solvers today suffers from bad decisions during their warm-up period, whereas GQSA T has been trained to examine the structure of the particular problem instance to make better decisions at the beginning of the search. Training GQSA T is data efficient and does not require elaborate dataset preparation or feature engineering to train. We train GQSA T on small SA T problems using RL interfacing with an existing SA T solver. We show that GQSA T is able to reduce the number of iterations required to solve SA T problems by 2-3X, and it generalizes to unsatisfiable SA T instances, as well as to problems with 5X more variables than it was trained on. We also show that, to a lesser extent, it generalizes to SA T problems from different domains by evaluating it on graph coloring. Our experiments show that augmenting SA T solvers with agents trained with RL and graph neural networks can improve performance on the SA T search problem. 1 I NTRODUCTION Boolean satisfiability (SA T) is an important problem for both industry and academia impacting various fields, including circuit design, computer security, artificial intelligence, automatic theorem proving, and combinatorial optimization. As a result, modern SA T solvers are well-crafted, sophisticated, reliable pieces of software that can scale to problems with hundreds of thousands of variables (Ohrimenko et al., 2009). SA T is known to be NPcomplete (Karp, 1972), and most state-of-the-art open-source and commercial solvers rely on multiple heuristics to speed up the exhaustive search, which is otherwise intractable. These heuristics are usually meticulously crafted using expert domain knowledge and are often iterated on using trial and error. In this paper, we investigate how we can use machine learning to improve upon an existing branching heuristic without leveraging domain expertise.

Most state-of-the-art satisfiability (SA T) solvers are capable of solving large application instances with efficient branching heuristics. The VSIDS heuristic is widely used because of its robustness. This paper focuses on the inherent ties in VSIDS and proposes a new branching heuristic called TB-VSIDS, which attempts to break the ties with the consideration of the interplay between the branching heuristic and learned clauses. However, a branching heuristic cannot cover all problems, and its performance improves when combined with an appropriate configuration. Therefore, we also propose a hybrid model of branching heuristics based on random forest. The efficiencies of TBVSIDS and hybrid branching heuristics are evaluated on benchmarks in SA T Competitions. By constructing a model that reduces the overfitting problem, we hope to realize a hybrid branching heuristic that is widely applicable to other solvers.

Modern conflict-driven clause-learning SAT solvers routinely solve large real-world instances with millions of clauses and variables in them. Their success crucially depends on effective branching heuristics. In this paper, we propose a new branching heuristic inspired by the exponential recency weighted average algorithm used to solve the bandit problem. The branching heuristic, we call CHB, learns online which variables to branch on by leveraging the feedback received from conflict analysis. We evaluated CHB on 1200 instances from the SAT Competition 2013 and 2014 instances, and showed that CHB solves significantly more instances than VSIDS, currently the most effective branching heuristic in widespread use. More precisely, we implemented CHB as part of the MiniSat and Glucose solvers, and performed an apple-to-apple comparison with their VSIDS-based variants. CHB-based MiniSat (resp. CHB-based Glucose) solved approximately 16.1% (resp. 5.6%) more instances than their VSIDS-based variants. Additionally, CHB-based solvers are much more efficient at constructing first preimage attacks on step-reduced SHA-1 and MD5 cryptographic hash functions, than their VSIDS-based counterparts. To the best of our knowledge, CHB is the first branching heuristic to solve significantly more instances than VSIDS on a large, diverse benchmark of real-world instances.