Author: Russell Reagan
Date: 21:54:29 08/20/02
Go up one level in this thread
On August 21, 2002 at 00:18:40, Robert Hyatt wrote: >On August 20, 2002 at 22:44:28, Russell Reagan wrote: > >>On August 20, 2002 at 21:52:05, Robert Hyatt wrote: >> >>>That's backward. A hash hit near the root saves a _huge_ amount of work. >>>Just think how big the sub-tree is one ply away from the root, compared to >>>the sub-tree one ply away from a tip position... >> >>His concern was that a false hash hit near the root would cause a blunder. If >>you didn't probe for the first (say) 2 plies, you'd still get that same result >>from the hash hit you got at ply 3, right? Maybe I'm not thinking about it >>correctly, but as far as I can tell, the only *extra* work you're doing here is >>a 2 ply search, which is nothing. Unless I'm missing something (which wouldn't >>be the first time...) >> >>Russell > > >You are doing a (say) 12 ply search. If you probe at ply=2 you might get a >false hit, or not. But if you get a hit of any kind, you stop that branch at >ply=2 and avoid a 11 ply search. > >That is a _lot_ of work to avoid... What's the difference if you spend 0.001 seconds searching the first ply and then get a 10 ply hit instead? You aren't gaining an extra ply, since the 11th ply was the first ply that you spent basically zero time searching. Even if you searched 8 ply and got a 3 ply hit, you're still saving a _lot_ compared to the amount of searching you did to get to the 8th ply, right? I could say the same thing about null move. You are doing a 12 ply search, and you do a few million "shallow" searches to test your null moves. I could sit here and make it sound like null move is a piece of trash because its going to use a _lot_ of work to do a few million shallower searches. You of course know that's not the case, but to someone who was new to computer chess, you can say things like this and make them believe it. In this case, I'm the guy you could make believe it, so I'm wondering what (if anything) is the drawback to NOT probing at ply 1 to avoid a (probably) fatal blunder if you get a false hash hit. 1 in 1,225 is a lot better chances of surviving the false hit than 1 in 35. If you increase it to no probing in the first three plies (still nothing in comparison to the full search), your chance of blundering from the false hit go to 1 in 42,875 (all using 35 legal moves per ply). It seems to be that as long as you didn't probe in the first couple of plies, it is highly unlikely that you will suffer any consequences. If you're probing at the first ply, your chances are 1 in about 35 that a false hit will be fatal. Maybe I'm missing something as far as the statistical analysis goes. I never was very good with statistics. I guess the other possibility is that the actual probability that you will suffer on the first ply false hit is (1/35)*(probability of a false hit)? In that case, your odds are much better at ply 1. Hmm...you're the one with the PhD. Maybe you can figure this out :) Russell
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