Author: Charles L. Williams
Date: 09:45:28 05/05/99
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On May 05, 1999 at 11:32:15, KarinsDad wrote: >On May 04, 1999 at 23:40:34, Peter McKenzie wrote: > >[snip] >> >>How is your move ordering? Expect your nps to drop as your move ordering >>improves. > >I keep hearing this type of statement, but I haven't figured out the reason for >it. Could someone tell me the rational behind this? > >As to my move ordering, I have a sophisticated one in the design spec, but at >the moment, we have a simple one of pieces most likely to be moved in chess >first, other pieces later. The order is the same throughout the entire game (at >this point of the implementation). > >KarinsDad :) Move ordering requires a sort to be performed first. To do the sort, a list of moves needs to be generated. This takes time. With improved move ordering cutoffs happen sooner, which means less nodes evaluated. However, the moves are still generated. Although the nps (board positions) evaluated decreases, so does the overall time to do the search. If you change your alpha-beta to a negamax while keeping the eval the same, your nps should increase for this reason. In short, with good move ordering, there is a slight inefficiency because a lot of moves that will never become a node need to be generated up front for the sort. I'm on my first cup of coffee and recovering from a cold, so this might not make a lot of sense. :) Chuck
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