NegaScout & TT
Author
Hi,
I use NegaScout along with Transposition Table but I don't save results obtained via calls with zero-window: alpha, alpha+1. In fact I don't use TT in zero-window search at all. I'm not sure but I think saving these results may lead to mistakes. Can I somehow make use of zero-window search result in context of transposition table?
You should definitely store and use the results of zero-window searches. If you also store a flag indicating whether the stored result is an exact score, a lower bound or an upper bound, this shouldn't lead to any mistakes.
Some pseudo code:
Some pseudo code:
int NegaScout(Board &b, int depth, int alpha, int beta) { if (depth<=0) return static_eval(b, depth); HashEntry *he = hash_search(b); if (he != 0) { if (he->depth >= depth) { // Don't use the score otherwise switch (he->flag) { case LOWER_BOUND: alpha = max(alpha, he->score); break; case UPPER_BOUND: beta = min(beta, he->score); break; case EXACT_SCORE: return he->score; } if (alpha>=beta) return alpha; } } // The loop goes here. Make sure to search the move stored in the hash table // first, even if (he->depth < depth). Also, break out of the loop in case of // a beta cut-off, instead of simply returning the score. This will give you // an opportunity to update the hash table, the history-heuristic table, etc. HashFlag flag = (best_score <= alpha) ? LOWER_BOUND : (best_score >= beta) ? UPPER_BOUND : EXACT_SCORE; store_hash(b, depth, score, flag, best_move); return best_score;}This topic is closed to new replies.
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