On the Optimality of Randomized $\alpha$-$\beta$ Search

  • Authors:
  • Yanjun Zhang

  • Affiliations:
  • -

  • Venue:
  • SIAM Journal on Computing
  • Year:
  • 1995

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Abstract

It was shown that the expected number of leaves evaluated by randomized $\alpha - \beta$ search for evaluating uniform game trees of degree $d$ and height $h$ is $O((B_d)^h)$ where $B_d = d/2+\ln d+O(1)$. It was shown by Saks and Wigderson [Proceedings of 27th Annual Symposium on Foundations of Computer Science (1986), pp. 29-38] that the optimal branching factor of randomized algorithms for evaluating uniform trees of degree $d$ is $B^{\ast}_d= (d-1+\sqrt{d^2+14d+1}\,)/4= d/2+O(1)$. As $B_d/B^{\ast}_d=1+O(\ln d/d)$, randomized $\alpha$-$\beta$ search is asymptotically optimal for evaluating uniform game trees as the degree of tree increases.