2018GlucoseHack中对变元活跃度的计算方法LRB和CHB做了统一的讲解，并提出组合LRB和CHB并简化的方法。
暂且简要记录在这里，留待后续结合代码认真研究。
1.文献见2018年sat竞赛的总结说明文档：
AbcdSAT and Glucose hack: Various Simplifications and Optimizations for CDCL SAT solvers
Jingchao Chen
School of Informatics, Donghua University
2999 North Renmin Road, Songjiang District, Shanghai 201620, P. R. China
chen-jc@dhu.edu.cn
2.主要内容
I. I NTRODUCTION
In this article, we focus on how to simplify the existing
techniques such as variable branching heuristic and learnt
clause reduction etc. VSIDS (Variable State Independent De-
cay Sum) is a prevalent decision variable branching policy. The
learning rate based branching heuristic (LRB) [9] proposed
in the recent year can outperform in some cases. So we
decide to simplify the LRB heuristic. The existing three-tiered
learnt clause management scheme is sophisticated and difficult
to use. Here we simplify it into a one-tiered learnt clause
management scheme so that a general CDCL SAT solver
can use it also. In addition, we introduce a new re-learning
technique.
II. S IMPLIFYING L EARNING R ATE B ASED B RANCHING
H EURISTIC
