Author: Ryan B.
Date: 15:07:33 02/15/06
Go up one level in this thread
On February 15, 2006 at 17:52:35, Nathan Thom wrote: >My engine is still very young (aptly named LittleThought) and I'm having some >issues explaining its behaviour. Features so far: >- Iterative Deepening >- AlphaBeta with limited move ordering (only captures are scored so far, with >SEE) >- Eval is simply material+piece sq >- Q search non-losing captures+checks+proms >- No hashing, no extensions, no pruning > >I just put in the Q search and a test run of 20 secs from the opening gives: > >With Q Search > >00:00:00.00 20n 1/1 0.58 1. e4 >00:00:00.01 512n 2/2 0.08 1. e4 d6 >00:00:00.01 2364n 3/4 0.00 1. h3 h6 2. g3 >00:00:00.03 9224n 4/6 0.00 1. h3 h6 2. g3 h5 >00:00:00.18 88Kn 5/9 0.00 1. h3 h6 2. g3 h5 3. f3 >00:00:00.65 361Kn 6/17 0.00 1. h3 h6 2. g3 h5 3. f3 h4 >00:00:12.97 8628Kn 7/37 0.00 1. h3 h6 2. g3 h5 3. f3 f5 4. e3 >00:00:20.00 13Mn 8/38 0.00 1. h3 h6 2. g3 h5 3. f3 f5 4. e3 >Total Nodes = 994854 >Total Q Nodes = 866141 >Total Beta Cuts = 99773 >Total Q Beta Cuts = 459231 > >Then I wanted to see how deep it could get without Q search, assuming it should >get further due to less Q nodes searched: > >Without Q Search > >00:00:00.02 20n 1/1 0.58 1. e4 >00:00:00.05 512n 2/2 0.08 1. e4 d6 >00:00:00.08 10Kn 3/3 0.56 1. e4 d6 2. d4 >00:00:00.31 148Kn 4/4 -0.05 1. Nf3 d6 2. e4 e5 >00:00:02.23 1468Kn 5/5 0.93 1. e4 e6 2. Bc4 d6 3. Bxe6 >00:00:20.00 16Mn 6/6 -0.42 1. d4 Nf6 2. Nf3 Nc6 3. e4 Nxe4 >Total Nodes = 2709329 >Total Q Nodes = 0 >Total Beta Cuts = 184327 >Total Q Beta Cuts = 0 > >This really surprised me and I still cant explain it properly. It searched more >nodes overall but to a lesser depth. My feeling is that its to do with beta >cutoffs and the Q search was somehow causing more of them, but after counting >them I see that the beta cuts within the normal search tree is actually less >when Q search is turned on. > >I'm sure its somehow related with the fact that the Q search seems to return >scores of 0.0 all the time (which sounds right as the opening is very stable) >and without the Q search, the scores seem to alternate +/- depending on who made >the last move. Also without the Q search, the moves seem to be smarter and make >use of the piece square tables more. > >Does it sound like a bug, or is this expected behaviour? Not a bug, because of the qsearch you are getting more reliable scores causing quicker cutoffs and a more stable search. Also people may be surprised that if the knowledge is good some times added chess knowledge helps search depth for the same reasons. Ryan
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