Author: Vincent Diepeveen
Date: 04:35:38 11/24/98
Go up one level in this thread
On November 24, 1998 at 03:02:51, David Blackman wrote: >On November 23, 1998 at 09:20:43, Robert Hyatt wrote: > > >>It's not as bad as it sounds, because remember that I said to search the *other* >>moves to D-2. If the fail high search costs you X nodes, then the extra tests >>on the moves you would normally look at will only cost you w/w^(D=2) nodes >>which lets you constrain the cost quite a bit. It certainly isn't free, but >>it doesn't double the size of the tree or anything close to that... >> >>ie if your normal branching factor (W) is 36, then the tree will grow by a >>factor of about 1/36... not too bad.. > >Are you sure about that? Given that you're still using alpha-beta i'd have >thought the cost of checking the extra moves was about >w * w^((D-2)/2) >compared to finding the initial fail high at >w^(D/2) >ie, about the same. >Although i could be missing something due to failing high and failing low having >different costs. > >Certainly, when i attempted singular-move extensions a few years back i found >that detecting singular moves was often more expensive than doing the extension. > >However i only did a one-ply extension. I think Deep Blue does a 2 ply extension >in most cases. > >I briefly considered always doing the extension, without checking if it was >singular, but then i decided that was silly. > >I guess you could reduce the cost of detecting singular moves a bit by cutting 3 >or more plies off the depth, instead of just 2. > >I think i tried that at one stage. It's nice for tactical problem sets, but not >clear if it actually helps in real games. Doing singular extensions reducing depth too much doesn't make sense, because for tough problems you need a huge depth left to detect whether it is a singular move. The most difficult singular moves are only singular after a huge depth left to search. Meaning that if you reduce a lot, that you will miss an awfull lot of interesting singular moves. A good example is in the bs2830 test set the move Qb7-d5, which with singular extensions depth reduction = 0, could be found at say 6 ply. Please turn off all other extensions, just use singular extensions, and report back how deep it takes then! This problem is found by most programs not because of singular extensions, but because of other extensions such as passed pawn extensions, recapture extensions, and check extensions. If the combination of all extensions find it soon, then how much would it take to find it WITHOUT singular extensions and with the extensions used? So there are 4 ways to test a) all extensions off, SE on b) all extensions on, SE on c) all extensions on, SE off d) all extensions off, SE off (which is the most uninteresting) The most interesting is to compare b with c. In fact S.E. should find this really quickly, but when i test this with S.E. on, then i'm suffering horrible from the reduction factor, which misses the advance of the c-pawn. In fact i find this move easier then without S.E. than with, as it eats up too many plies extending nonsense. here is the position (bs2830-26): 1r4k1/1q2pN1p/3pPnp1/8/2pQ4/P5PP/5P2/3R2K1 b - - Qd5
This page took 0 seconds to execute
Last modified: Thu, 15 Apr 21 08:11:13 -0700
Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.