Author: Robert Hyatt
Date: 17:20:54 08/04/99
Go up one level in this thread
On August 04, 1999 at 10:44:06, KarinsDad wrote: >On August 03, 1999 at 19:27:18, Ricardo Gibert wrote: > >[snip] >>> >>>If you are in a mate in 110 situation (probably extremely rare), it would >>>probably behoove you to do your own searching for capture/push moves that lead >>>to positions that maintain the win since you will probably find them relatively >>>close to the main line anyway. Compared to searching even something as simple as >>>an 8 ply alpha-beta, searching for those moves would take VERY little time. The >>>reason this works out so well is that you do not have to search outside the >>>tablebase once you are in it (or once you are close enough to it to force your >>>way into it). >> >>In many pawnless EGs a "good" capture can be hard to come by. 8 ply would not do >>it in that case. >> > >One other note on this. When you have moves that lead to mate, but they lead to >mate 110 moves (i.e. 220 ply, I believe this is what you were trying to discuss) >later, you have the option of searching for win preserving moves at ply 1, ply >3, ply 5, etc. Everytime it is your turn, you can attempt to find a win >preserving move which has a pawn push or a capture. > >Granted, you will not be able to search REAL far each time, but even if you only >had a second per move, it would take at most two minutes total to search down 6 >ply each and every time (i.e. 50 times at ply 1, 3, 5, 7, etc. for a maximum of >about 120 moves or 240 ply for your 220 ply best case) before a capture or push >was needed. This assumes that you can load up a given 5 piece tablebase into >memory (or most of it) and use it (since you will be in a position of not >capturing, you will continue to be in the same tablebase). It also assumes that >you can search just as far into a tablebase as you could search normally in your >search/eval which on the surface, appears to be a slam dunk assumption. Most >likely, you could search even faster and farther with the tablebase. > stop just a minute and think about what you just said. You _really_ think you can do a 220 ply search? Because that is _exactly_ what you have to do to follow that tablebase search to the end to handle 50 move and rep correctly. The tablebase contains _all_ possible positions. So if it says mate in 220, which some 6 piece files will definitely do, you are going to have to search far farther than you think to find that playable capture or pawn push. So far that it will be beyond our capability for at least a few zillion years. :) >Anyway, my basic point is that you would not HAVE to search far. Sooner or >later, you would most likely find a win preserving move within 6 or 8 ply >(depending on how much time you have and how far you can search the tablebase) Lewis Stiller disproved this. He found lots of positions where a playable pawn move (or capture) happened more than 70 full moves from the original position. It would be absolutely impossible to search 140 plies in a 6 piece ending. It would be impossible to search even 60 plies in most of them unless they are all pawns and they are locked up totally... >since you have 50 of your moves (99 ply) in which to "get lucky". It should >happen eventually almost every time (although there may be some extreme cases >where it would not). The bottom line is that this approach would win extremely >rare games that broke the 50 move rule, but at the same time would not introduce >a major change into the tablebases. > >KarinsDad :)
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