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Revisiting Check Extensions
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Mark Lefler



Joined: 30 Mar 2006
Posts: 500
PostPost subject: Re: Revisiting Check Extensions    Posted: Sun Jun 10, 2007 7:34 am Reply to topic Reply with quote
[quote="bob"]
mjlef wrote:
bob wrote:
mjlef wrote:


Basing this on material has a couple of dangers:

(1) if you don't extend checks that lose material, what happens to you on positions like WAC 141 where the key move tosses the queen for no apparent gain?


I see no reason why people here keep giving single exceptional positions when new ideas are presented. Of course you can find expections to rules and find some positions where the rule might not work as well as what had been done before. What I quoted was my results in hundreds of real games. Of course some sacrifical checks can lead to wins, but overall, the extra search depth of not extending on them so much seemed to help Now. Tossing queens away is generally foolish. Instead of citing single examples, how about some test runs in games?

I frankly think most tactical test sets are not very useful in making programs play better. Most are loaded with "lets throw away a lot of pieces and force a mate in an unexpected way". I have extensive tests and statistics I have gathered and they show most sacrifices are just sacrifices and lead to bad play. Isn't that how most programs qsearch works... apparently losing moves are tossed? My past obsessions with trying to do better on tactical test sets probably never lead to a program strength increase. Although some changes, say in speeding up a move generator or evaluation, can use a tactical test to show an increase.

I am not trying be critical...I just have grown slightly tired of people implying one example disproves a larger idea. I do find some examples very useful, and I encourage them...but I would really prefer replies like "I tried your idea back in 1995 and my program did not benefit, as these test results show...."

Mark


I'm not giving "single exceptions". I just gave you _one_ position.. How many would you like? The majority of chess combinations are based on a sacrificial theme don't forget. And those are the very positions where you need to be sure that you are really material ahead, or material behind, not use either of those as a justification for not looking deeper.

That was my point. Search however you want of course... But there are risks.


The number of examples is rather meanlingless unless placed in the context of real games. Losing captures are rarely the best move in a position. My stats gathered from thousands of searches show about 0.1% of the time are losing cpatures the best move, on average compared with over 70% of the time for winning captures. Losing capture checks have similar stats. What is important is is the increase in nodes under the extension point worth the extra effort expended. Is it likely to change the PV?

I think some good rules could be included to allow some extensions fo losing captures. Right now I do extend losing capture slightly if they lose les then 1.5 pawns. A sacrifice exposing the opponent king could be worth extending even if it loses material, and that is something I am testing. Maybe always extend check on expected PV nodes makes sense. My goal is not to do well in tactical combinations. It is to do well in real games.

I know many programmers say "always extend all checks"...but why do they say that and what data do they have to back it up?

Mark
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Subject Author Date/Time
Revisiting Check Extensions Mark Lefler Thu Jun 07, 2007 9:25 am
      Re: Revisiting Check Extensions Uri Blass Thu Jun 07, 2007 10:19 am
            Re: Revisiting Check Extensions Tord Romstad Thu Jun 07, 2007 10:33 am
                  Re: Revisiting Check Extensions Uri Blass Thu Jun 07, 2007 10:59 am
                        Re: Revisiting Check Extensions Uri Blass Fri Jun 08, 2007 8:37 am
                              Re: Revisiting Check Extensions ed Fri Jun 08, 2007 9:40 am
                                    Re: Revisiting Check Extensions Uri Blass Fri Jun 08, 2007 10:06 am
                  Re: Revisiting Check Extensions José C. Martínez Galán Thu Jun 07, 2007 11:01 am
                  Re: Revisiting Check Extensions H.G.Muller Thu Jun 07, 2007 11:59 am
            Re: Revisiting Check Extensions Mark Lefler Thu Jun 07, 2007 1:05 pm
      Re: Revisiting Check Extensions Robert Hyatt Fri Jun 08, 2007 3:25 pm
            Re: Revisiting Check Extensions Tony Fri Jun 08, 2007 3:50 pm
                  Re: Revisiting Check Extensions Robert Hyatt Fri Jun 08, 2007 4:03 pm
                        Re: Revisiting Check Extensions Tony Fri Jun 08, 2007 7:28 pm
            Re: Revisiting Check Extensions Mark Lefler Sat Jun 09, 2007 8:04 pm
                  Re: Revisiting Check Extensions Robert Hyatt Sat Jun 09, 2007 9:59 pm
                        Re: Revisiting Check Extensions Mark Lefler Sun Jun 10, 2007 7:34 am
                              Re: Revisiting Check Extensions Uri Blass Sun Jun 10, 2007 7:46 am
                              Re: Revisiting Check Extensions Robert Hyatt Sun Jun 10, 2007 3:25 pm
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