Author: Robert Hyatt
Date: 11:52:53 01/25/00
Go up one level in this thread
On January 25, 2000 at 13:28:33, Christophe Theron wrote: >On January 24, 2000 at 16:05:00, Robert Hyatt wrote: > >>On January 24, 2000 at 15:34:39, Christophe Theron wrote: >> >>>On January 24, 2000 at 09:10:12, Robert Hyatt wrote: >>> > >(snip) > >>>I'm really curious about this. Using a SEE to "close" the search is in my >>>opinion a beginner's mistake (no offense intended). >>> >>>It's the first thing I have done myself when I started programming chess, and I >>>suspect many of us have followed the same path. >>> >>>But if somebody tells me it really works, then I have, once again, to reconsider >>>seriously all I know about chess programming. >>> >>>It's not new anyway. Every now and then I realize how little I know. That's part >>>of the fun. >>> >>> >> >> >>Good question. I did this around 1972 or so, and found it was a great addition >>since I couldn't afford a q-search at the speed of 10 nodes per second or so. I >>too dropped this around 1978 when I went "full-width + q-search" to become yet >>another "clone" of chess 4.x after the Frey book came out. >> >>I'll let the 'author' of the suspected non-q-searcher speak up if he wants, >>to avoid starting a long "did, did not, did too" type discussion. I am not >>sure it is totally bad with a decent search in front of it. When I did it I >>was doing a 4-5 ply selective search. It was ok. I went to a 4-5 ply full- >>width search. It was not ok after that. Maybe after 13-14 plies it is OK >>again? > > >I think the SEE idea is not good because on deep searches the QSearch typically >is very quick, looking at a very reduced number of nodes in average (maybe one >or two nodes is enough in most cases). > >If your make/unmake move and evaluation is fast enough, this is going to be much >faster than using a SEE in this position. Because to be reliable a SEE has a lot >of work to do (bitboarded or not). Maybe or maybe not. I have not (personally) given it any thought, and don't plan on doing so. I used it a long time ago (20+ years) to see if the _last_ move in the tree was safe or not. With a fixed depth (more or less) search, the last move was always suspect, as it would be a capture of something where there was no way to recapture since the search had maxed out. SEE could make sure that you weren't planning on winning a pawn, just to lose the queen or whatever. I didn't do it on _all_ my pieces, just on the one moved at the final move in the PV. I suppose you could do something more clever... as SEE is way faster than any sort of tree search, if done as I did above... IE my SEE code takes less time than it does to recursively call search, generate moves, etc... But if I tried to do it for several pieces, I think it would be too slow. > >Another thing is that a QSearch is more accurate than a SEE. Being accurate is >important, because it makes your tree smaller. If your SEE is wrong often >enough, then the next ply depth is going to have some extra work to do because >the last time you have found this position (a position near the horizon) you >actually did not find the best move. Your move ordering near the horizon is less >good with a SEE, and this is expensive. > >I have actually found several cases in my program where looking at a bigger >potential tree was actually faster than trying to reduce the potential tree. > >Very often, an algorithm that has a bigger potential tree runs faster than a >reduced potential tree algorithm, because it extracts more accurate information. >And when you go to the next ply depth, the accurate information is extremely >efficient. > >The most interesting example for me is that without QSearch my program is much >slower (and of course less accurate). > >Search+QSearch has a bigger potential tree, but is far better (and actually >faster) than Search alone. maybe or maybe not. remember that one program is apparently doing this and it is _very_ strong. That is the only reason I gave it even a minute's thought in this discussion, as it is working for someone... > >This is counter intuitive, but very interesting. When I realized that, I was >able to think differently. > > > Christophe
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