Author: Sune Fischer
Date: 04:14:55 04/21/04
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On April 21, 2004 at 05:44:51, Tord Romstad wrote: >On April 20, 2004 at 19:57:00, Sune Fischer wrote: > >>>I used to do static mate detection in the past, but had to sacrifice it when >>>I simplified my attack tables. >> >>As always it's a trade off, your new tables are probably faster? :) > >Yes, though not very much. The effect on playing strength seemed to be more >or less neutral. When there is no measurable difference in strength between >two different ways to do something, I tend to prefer the simplest solution, >in order to reduce the number of potential bugs. I figured the easiest of all was to get rid of them entirely. :) >>>This is strange. I have very rarely seen something like this. Do you have >>>any examples of positions where this occurs? How much did you extend for >>>mate threats? >> >>It happens pretty much in all attacking positions, eg. wac141 takes a lot longer >>to solve with null-threat extension on. >>I use half a ply for the extension. > >Have you tried to make this more dynamic, like I do? I haven't tested this >very thoroughly, but intuitively it seems plausible that it is more useful >to extend for mate threats when the side to move has an advantage. It might >be a good idea to let the amount of extension depend on the static eval. Yes I have tried this. The result on wac141 is that it still finds the right move fast, but efter that it has a high score and takes forever to find the mate. I'm not convinced that the overall effect is a good one, once you really have a hold of your opponent it is better to kill him off sooner rather than later. (see also my post to Uri) >Very strange. Here are my results for WAC141 with mate threat extension >on and off: > >Mate extension on, BM extension on: Solved in 6 plies, 13380 nodes. >Mate extension on, BM extension off: Solved in 7 plies, 48236 nodes. >Mate extension off, BM extension on: Solved in 9 plies, 156929 nodes. >Mate extension off, BM extension off: Solved in 9 plies, 156937 nodes. > >As you can see, the combination of mate extensions and BM extensions helps >Gothmog find Qxf4 3 plies earlier, and in less than 10% of the nodes. This >is by no means unusual in such positions. Mate extensions improve the speed >tremendously in positions where checkmates are important, and seems to have >very little cost in other positions. Strange, I can't reproduce this effect at all. I've read of others who didn't get anything from this so I though it was normal. >I had very strange results with the BM extension. I found very few test >positions where Gothmog performed better with the extension enabled, but >when playing games the version with the extension consistently scored >slightly better. Oh that is interesting, I don't think I ever gave it a chance in real play because it didn't seem to work even on position where I thought it should work. >I haven't noticed this problem very often. It probably depends on your move >ordering. In the node following a null move, if the null move failed low >by a big margin two plies earlier, I search the last refutation move directly >after the hash table move. Yeah it could be related to move ordering, although the extension is used in Crafty and Crafty doesn't have this kind of move ordering. I also tried searching the refutation move first, but it didn't have a very high cutoff percentage. I feared that searching it first would reduce general move ordering and searching it later would trigger a lot of needless threat extensions on the first moves. -S. >Tord
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