Author: Will Singleton
Date: 18:23:30 02/25/99
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On February 25, 1999 at 19:45:50, John Stanback wrote: >On February 24, 1999 at 19:16:27, Bruce Moreland wrote: > >> >>On February 24, 1999 at 15:37:58, Don Dailey wrote: >> >>>My program is a mixture of static rules and null move. I do null >>>move when I have significant depth remaining, but when I am near >>>end nodes I do a simple static attack analysis. This has proven >>>to be a significant improvement to my chess program. It is faster >>>than null move and slightly riskier, but the net affect is >>>a stronger chess program (for me.) Even though it's probably >>>riskier, it does pick up things null move will miss although the >>>converse is also true. >> >>Can you describe this or give examples please? I know that some people do this >>but I haven't the vaguest idea how it works. >> >>bruce > >In Zarkov, I also use a combination of null move search and static >evaluation to selectively prune the tree. At depths 4 and higher I >use standard null-move search with R=2. Like Don, at depths 1-3 if >the static eval is greater than beta+margin then I use static >threat detection (and sometimes depth reduced searches) to try to >prune the tree. On some problems this works better than null-move and >sometimes worse. Overall I've gotten a little better results. >Some of the threat detection stuff is a little "ugly", but whatever >works... :) > >I first discovered the simple heuristic approach to selective search >in 1988 and like Don I couldn't believe that I had worked on my program >for years without thinking of this. It's that mythalogical one line >change that gives a huge increase in strength that every chess >programmer dreams of -- except that it doesn't actually give a huge >increase in strength (at least not without adding the threat detection >stuff). Anyway, when I first tried adding this line to the search >routine (at all depths) I was elated: > >if (static_eval > beta) return(beta); > >Even on my old 8 Mhz 286 Zarkov now cruised through the iterations, >giving some pretty nice looking PV's. WOW! Let's try some problems. >OOPS, it can't solve anything. Well, so maybe the static eval isn't >quite good enough, the next step is to add some threat detection stuff >to try to fix the problem :). This selectivity is actually the same >idea as null-move, except much riskier and trickier to implement. >Anyway, it's great fun to add the line above and see how fast the >search goes. > >What do most null-movers do at depth=1? > > >John I don't use null move at depths 1, so I'm looking forward to trying this "static selectivity tester", as Don put it. Will
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