Author: Roberto Waldteufel
Date: 13:38:43 05/04/98
I have read about the singular move extension heuristic as used by Deeper Blue, and indeed about extension heuristics in general. I have also experimented with some variable depth schemes in my search trees. One quite promising idea is to set the depth to some arbitrary value at the start of each iteration (this value being increased a little prior to each successive iteration), and then decrease the depth at each odd level by an amount proportional to the logarithm of the number of legal moves for the opponent at that level, and calling a quiescence search when this depth drops below zero. The depth remains unchanged at even levels. This has the effect of pusuing forcing lines for the machine much deeper, even if some quiet moves are interspersed between the checks. It works very well for some tactical positions where the machine can mate or win material through a long sequence of moves, most, but not all of which are checks. I understand that in the singular move extension scheme, the node is extended if its evaluation is significantly higher than that of its next-best sibling, but I do not understand exactly how this condition can be tested when a beta-cutoff occurs, since the evaluation scores for some of the sibling nodes is then not known to the algorithm. Can anybody enlighten me? Robeto Waldteufel
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