Author: Nathan Thom
Date: 14:52:35 02/15/06
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?
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