Author: Dan Newman
Date: 10:17:33 11/30/00
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On November 28, 2000 at 13:34:30, Robert Hyatt wrote: >On November 28, 2000 at 12:52:57, Scott Gasch wrote: > >>Hi, >> >>I posted a couple of messages about move ordering yesterday and wanted to share >>some results from my (limited) testing. I ended up implementing the suggested >>"apparently losing captures" (MVV/LVA) after all others order. In one test >>position this resulted in a tree 200k nodes larger at 8 ply but in two others it >>resulted in a marginally smaller (under 40k nodes) tree at 8 ply. I will do >>more testing on this matter but it may be a moot point because I intend to write >>a SEE pretty soon. >> >>I also did some experimenting with ordering captures that take the last moved >>enemy piece. At low search depth this seems to make some difference but at >>higher depth this heuristic actually grew the tree in all three test positions I >>tried. >> >>I also did some playing with history weight and settled on hist[x][y] += (2 << >>depth). My numbers (this is total nodes searched until ply x including plys >>1..x-1) for d2d4 d7d5 e2e4 e7e5 are currently: > >Just a note. 2<<depth is not a good idea. what happens if you search to 32 >plies? This is more than possible with today's hardware. Unless you are using >a 64 bit integer. I ran into trouble with this some time ago. The move ordering goes bad when the history table entries overflow. I switched to depth * depth after seeing it in Crafty--I'd tried a bunch of other things that didn't work too well. I now use (depth * depth) >> 10 since I use fractional plies. IIRC, I found some overflows with plain depth squared... -Dan. > > > >> >>1. 45 >>2. 621 >>3. 3725 >>4. 14146 >>5. 38694 >>6. 183449 >>7. 598020 >>8. 1286875 >> >>I am doing null move (R=2/3 depending on remaining and normal futility pruning >>with a slightly larger than safe window on frontier nodes and in qnodes. I've >>read about extended futility pruning and razoring too. I'd be interested in >>other ideas to cut down the tree search size... be they other move ordering >>heuristics or other pruning methods that are reasonably safe. How do the nodes >>searched in the position given compare to other engines? >> >>Thanks again, >>Scott
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