Author: Robert Hyatt
Date: 11:13:52 03/11/03
Go up one level in this thread
On March 10, 2003 at 17:43:30, Gerd Isenberg wrote: >On March 10, 2003 at 17:10:43, Tom King wrote: > >>On March 10, 2003 at 17:06:10, Gerd Isenberg wrote: >> >>>On March 10, 2003 at 14:49:30, Tom King wrote: >>> >>>>Hi all, >>>> >>>>One search extension which most programs seem to use is the passed pawn pushing >>>>extension. When a move is made which is a passed pawn push to the 7th rank, we >>>>extend the search by a ply. >>>> >>>>My programs has got away without this extension for years. Or perhaps "got away" >>>>isn't right.. there have been losses which this extension might have prevented. >>>> >>>>Anyway, what do people think of this extension. Worth having? If so, what value >>>>would you attach to it? >>>> >>>>Regards (and hi to all), >>>>Tom >>>>tom@silentshark.co.uk >>> >>>Hi Tom, >>> >>>i do some fractional extensions with passers. Not only if they push or capture >>>foreward to the 6th or 7th rank, even if a opposite "guard" pawn in backward or >>>knight distance (re)captures (but no push) from it's base rank (own 7th rank) to >>>the "right" side, which establish an own passer on the 6th rank. I consider the >>>number of advanced passers per side, supporting and defending pieces. A lot of >>>code, specially at interiour nodes or near the root to look for further >>>recuductions of determined extensions. >>> >>>Even if these extensions work fine in some testpositions, i requires a lot of >>>effort to tune them for tournament play. Most often i do it by "gut feel". >>> >>>One thing i tried to control extensions with is to vary the amount of fractions >>>to become one ply. I tried to vary it by search depth and by the relative amount >>>of extensions so far. >>> >>>Regards, >>>Gerd >> >>Hi Gerd, >> >>Sounds like your passed pawn extensions are very sophisticated - doesn't this >>analysis slow up your search? > >Yes, but for nodes with depth left > 0. For leave nodes i use simpler and faster >code so i believe it pays off. The final fractional depth remainder at leave >nodes triggers some qsearch features, to make the qsearch width dependend on the >remaining fractional depth, eg. check moves or an optional quite hint move (if >any) from eval. > >> >>I'm sure you are dead right about the test positions. I gave up with testsuites >>a while back, and now just use hundreds of test games to determine whether a >>change is beneficial or not. >> >>Regards, >>Tom > >That's the right way to do it - but there are so many screws and switches. >I still use some testpositions and during tournament play i'll hope let the >heuristics fit ;-) > >This position was sensible to passed pawn extensions for me. >After IsiChess lost the game againts Shredder in Maastricht after c3? i did some >extension (passed pawn reductions but some other additional extensions) and even >eval tuning to solve this - but don't ask me whether IsiChess is stronger now. > >[D] 8/k1p1r3/p2b3p/5ppq/1np5/6P1/1R1N1P1P/R4QK1 b - - ; am c3 > > >Regards, >Gerd This position seems to be less about passed pawns and more about king safety and check extensions. IE after c3, Rxb4 threatens Qxa6. Crafty says +2 here after only 4 plies and zero seconds, for example. I don't think the pawn on c3 means a thing here.
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