Author: Tord Romstad
Date: 08:35:54 07/28/04
Go up one level in this thread
On July 28, 2004 at 08:55:25, Uri Blass wrote: >On July 28, 2004 at 08:23:17, Tord Romstad wrote: > >>On July 28, 2004 at 07:06:22, Uri Blass wrote: >> >>>How much rating do you earn from dividing the evaluation by 4. >> >>I no longer remember exactly, but I think it was quite a significant >>improvement. However, it is possible that the improvement is mostly explained >>by a horrible futility pruning bug I introduced while doing the change. For >>some reason, this bug seems to make the engine much stronger, and all attempts >>to fix it have had catastrophic results. >> >>The bug is the following: >> >>In the qsearch, I prune futile captures with code that looks roughly like >>this: >> >>if(approximate_eval_after_move(move) < alpha-margin) >> prune move >> >>The approximate_eval_after_move() function takes the static eval of the >>current position and adds the change in material and piece square table >>scores when the move is made. When I changed from pawn=64 to pawn=32, >>I forgot to modify the approximate_eval_after_move() function. This >>function still divides by 2 rather than 4, and returns scores with >>unit pawn=64. > >If I understand correctly your function give twice the expected value instead of >giving the expected value. > >I guess that alpha is near 0 during the game. This can vary a lot, but OK. >Let assume that margin is near 1 pawn In most positions, this is not too far from the truth. I think it is usually slightly less. >If approximate_eval_after_move(move)<-1 pawn was planned. > >If 2*approximate_eval_after_move(move)<-1 pawn was done. >In other words >If approximate_eval_after_move(move)<-0.5 pawn was done. > >I suspect that it may be better to correct the bug and also divide margin by 2. >Did you try it? Yes, I have spent an enormous amount of time testing all sorts of settings. I haven't found any other setting which is even close to what I currently use. It's tremendously frustrating. Perhaps I should have a look at this problem one final time before I release Gothmog 1.0. Tord
This page took 0 seconds to execute
Last modified: Thu, 15 Apr 21 08:11:13 -0700
Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.