Author: Roberto Waldteufel
Date: 08:01:38 09/29/98
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On September 29, 1998 at 10:53:28, Don Dailey wrote: >On September 28, 1998 at 20:02:42, John Coffey wrote: > >>Looking at my copies of old threads maybe I understand better... >> >> >>Just because you're behind in material at a node, doesn't mean you >>won't regain (some of) it in the search below that node. Let's >>imagine that at a node you are behind in material, but are just about >>to deliver mate, and your opponent can't get out of it--even if he's >>given two moves in a row. The null move will return the mate score >>and give you an instant cutoff. Or imagine the oppenent can >>get out of it with those two moves, but only at the loss of a lot >>of material. Again you might get a cutoff. >> >>The null move works as long as the score returned by the null move >>search is greater than or equal to beta. What the current material >>is is...immaterial. >> >>-Dan. >> >> >>>>>>I try them _everywhere_ in the search, before trying any other move. The idea >>>>>>is that if your opponent can't take two moves in a row and crush you, your >>>>>>position is **overwhelming** and doesn't need any further searching to prove that >>>>>>it is probably winning... >> >> >> >> >>...... so even if we are behind in material, a null move search that gives >>my the opposite side two moves in a row could still produce a positive >>result? I.e. I was a rook down, but null move analysis shows that I am >>only a pawn down, chances are I am really crushing the opponent? If so, >>then does this return an evalation that we can use in the tree? >> >>John Coffey > >As was just pointed out to me recently, a simpler way (conceptually) >to view null move searching is to simply look at it as just another >move in the move list. For example, if you have 30 legal moves, then >view the null move (followed by a depth reduced search) as the 31st >move in the list (sorted to the front of course.) Sometimes this >move will give you a beta cutoff, other times it will simply provide >a "best move" which raises alpha and makes the remaining search >faster. > >I don't actually implement it just like this, but this is basically >sound it COULD be implemented this way with no problems. > >- Don Hi Don, I can confirm that this works fine. I recently added null move test in my program, and this is exactly how I implemented it. Best wishes, Roberto
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