Author: Vincent Diepeveen
Date: 04:44:06 02/24/99
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On February 24, 1999 at 02:30:21, Will Singleton wrote: >On February 24, 1999 at 01:16:56, Sylvain Lacombe wrote: > >> >>I just finished implementing the null move. At first, i thought it wasn't saving >>much time. Then, i reallize that it does save alot, but only at deeper plys. On >>the first few plys, i think, it evens slow me down. Is that normal? Am i doing >>something wrong? >> >>I don't use the null move at the first ply, only at the second. It save about >>40% reaching deep 6. But it takes about 10% more for reaching deep 3 and 4. >> >>Hope, you can help. >> >>Thanks. >> >>Sylvain. > >You're probably doing something wrong. But get a second opinion. :) > >My prog will use about half as many nodes early on, like up to ply 5, then the >effect becomes more pronounced, and in plys above 7 or 8 can show 2-3x >reductions. But it depends on the position. If there's a single best move, >there's more reduction than if the position is pretty quiet. So try it on a >couple of different test suites, like wac vs Bratko-Kopec. Or, use the >positional BK positions measured against the tactical ones (12 each). > >Of course you wouldn't use null on the first ply, that would make it kind of >hard. Are you using a reduction factor of 2? That's the most popular, it >seems. I'm testing R=3 now, seems to work OK. But stick with 2 to start. > >Also, make sure you don't do 2 nulls in a row. And, for testing purposes, you >should probably limit a null move to one per search (I mean, once the null has >been done, don't do it again below that node). Then when it's working better, >test out multiple nulls. > >Null moves are susceptible to zug positions, so just disable them in the >endgame. You can try out better things later. > >Don't do null when in check! > >There's an open question about allowing nulls in the pv, so look at that. And >make sure to clear the ep flag after a null. This is no open question. Of course always do nullmove. If it doesn't give cutoff then you still can see whether you need a mating extension. It saves for me a lot anyway. ALWAYS do nullmove, just take care you don't improve your alfa with it if it fails. Some do that, but i'm not a big fan of that. >Also, look at what depth you start to disable them. Try various depths, like 3, >2 and 1. > >Hope this helps. > >Will
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