Author: Jari Huikari
Date: 08:50:18 10/21/98
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On October 21, 1998 at 10:54:16, James T. Walker wrote: >If I understood a previous thread, Dr. Hyatt indicated that there is effectively >no move ordering done by most programs(At least Crafty)? Can anyone please >answer this for me?? It seems unreal that there would be no attempt to order >the moves so that the most promising moves were searched first. Move ordering is done. The most promising is searched first, but after that the ordering is not done using exact values. Alpha-beta doesn't find how much worse the rest of the moves are compared to the best one. The values calculated to all the other moves tell how much worse they are AT LEAST than the best one. (E.g. the best move M1 have the score +3.2, which is the real score for that move. For move M2 it's calculated that it's value can't be better than +2.0, and score for move M3 is found to be +0.5 or less. Calculations for M2 and M3 are not calculated to the end. +2.0 and +0.5 are upper bounds found for their values. They are sorted by these values. And it can be that real value of M2, if it were calculated to the end, would be -3.0 and M3 could be actually a better move. But much time is spared when calculations are stopped after finding that moves M2, M3, ... are just WORSE than M1. This is much faster than computing HOW MUCH WORSE they are. And even if all moves were calculated to the end, their order will be changed when searched deeper in later iterations. Jari
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