Extended Null-Move Reductions

  • Authors:
  • Omid David-Tabibi;Nathan S. Netanyahu

  • Affiliations:
  • Department of Computer Science, Bar-Ilan University, Ramat-Gan, Israel 52900;Department of Computer Science, Bar-Ilan University, Ramat-Gan, Israel 52900 and Center for Automation Research, University of Maryland, College Park, USA MD 20742

  • Venue:
  • CG '08 Proceedings of the 6th international conference on Computers and Games
  • Year:
  • 2008

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Abstract

In this paper we review the conventional versions of null-move pruning, and present our enhancements which allow for a deeper search with greater accuracy. While the conventional versions of null-move pruning use reduction values of R≤ 3, we use an aggressive reduction value of R= 4 within a verified adaptive configuration which maximizes the benefit from the more aggressive pruning, while limiting its tactical liabilities. Our experimental results using our grandmaster-level chess program, Falcon, show that our null-move reductions(NMR) outperform the conventional methods, with the tactical benefits of the deeper search dominating the deficiencies. Moreover, unlike standard null-move pruning, which fails badly in zugzwang positions, NMR is impervious to zugzwangs. Finally, the implementation of NMR in any program already using null-move pruning requires a modification of only a few lines of code.