Author: Ed Schröder
Date: 22:21:58 05/02/00
Go up one level in this thread
On May 03, 2000 at 00:17:28, blass uri wrote: >On May 02, 2000 at 07:38:08, Ed Schröder wrote: > >>On May 02, 2000 at 06:26:34, Michael Neish wrote: >> >>> >>>Hello, >>> >>>I wonder whether anyone could help me, or offer any suggestions as to the >>>following little problem. >>> >>>The program I'm writing needs two ply to see what I think should take only one >>>ply. >>> >>>In the position below White wins material by the blindingly obvious Bg5. >>> >>>[D]6k1/pp1nrppp/5rb1/P2P4/5BP1/5P2/4BK1P/R3R3 b - - >>> >>>However, if I set my program to look only one ply deep, it doesn't see this >>>move, and prefers Bb5. At two ply, though, it sees it all right. I think one >>>ply should be enough, as the Qsearch ought to take care of the ensuing >>>exchanges. Indeed, other programs I have tried manage to find it easily enough >>>in one ply. >>> >>>This might be a trivial position, but if it's taking longer than it should to >>>see these tactics then I could be wasting plies in my search. >>> >>>By the way, in case anyone asks, I'm not doing anything unusual in Qsearch. I >>>call Eval() first, return if it fails high, otherwise set alpha to the Eval() >>>score if it's greater than alpha, and then search through the available >>>captures. >>> >>>Thanks for your help. >>> >>>Mike. >> >>Rebel gives a bonus of 1.00 in eval for Bg5 assuming one of those rooks >>get lost. A higher bonus is quite risky as the opponent often has an >>escape. The effect in search is minor. It was effective in the days of >>programs running at 5 Mhz hiting 5-6 plies only. Nowadays I would not >>spend time on such (processor) time consuming cases. >> >>Ed > >I do not understand why not. > >If there is a long line when the final position is one of these cases >you can have a better evaluation. > >Usually long lines are not forced so the effect may be better positional moves >and not tactics. > >Uri Your point sounds very plausible but isn't true. Search solves these kind of cases and you only end up with some speed loss. Running a set of 500 positions only gave a few (non-important) different moves. That is one of the crazy things of CC, you have to go from scratch on your code every 3-4 years as many things that were good then are out-dated now because of increasing hardware (Mhz & Ram). A few days ago I wrote something about 1992 and one instruction making Rebel (The ChessMachine then) stronger. It made me think about and as a result I improved that piece of code with a net result of 28% speed gain. The change would not have been a good idea in 1992. Search is a strange animal and hard to understand for the human brain. It is full of unexpected surprises. I estimate that after 20 years wrestling with search I only understand 5% (or so) of search. Ed
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