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Check-extension in QS
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H.G.Muller



Joined: 10 Mar 2006
Posts: 21295
Location: Amsterdam

PostPost subject: Check-extension in QS    Posted: Fri Apr 03, 2015 5:37 pm Reply to topic Reply with quote

What is the consensus on check extensions during QS? In most of my engines, when I accidentally get checked by any of the captures, I usually search all evasions, also the non-capture evasions, i.e. extend to a d=1 search.

Is that really worth it, or could you just as well stand pat when in check, assuming that one of the non-capture evasions will keep you at the current eval? You will miss tactics where he can fork King + hanging piece through a capture (or that the check actually is a mate). But there could be lots of that through non-capture checks, which you would miss anyway. The chances that he could have such a fork by capturing anything should be slim. (I am talking now about the QS phase where you would not search non-capture checks in the parent node. Searching those would obviously not make sense if the opponent would be allowed to stand pat in the face of these.)

E.g. positions like the following:
[d]5rk1/5ppp/8/8/3Q4/2B5/8/8 b
   ::    ::    BR BK ::
::    ::    :: BP BP BP
   ::    ::    ::    ::
::    ::    ::    ::    
   ::    WQ    ::    ::
::    WB    ::    ::    
   ::    ::    ::    ::
::    ::    ::    ::    

If just before the horizon black in this position plays h6, Qxg7# would get him mated, but standing pat in the face of check would keep him unaware of that. But if he would be aware, he would play g6 just before the horizon, instead of h6. Then Qg7# would mate him just as much as before, but would not be searched in QS, and thus would look like a defense. So forcing black to search on after the capture check doesn't bring a thing if you don't allow searching the same non-capture check. He will just start to 'defend' by preventing the mating move is a capture. (Would be better eval-wise as well.)
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Subject Author Date/Time
Check-extension in QS H.G.Muller Fri Apr 03, 2015 5:37 pm
      Re: Check-extension in QS daniel jose Fri Apr 03, 2015 6:10 pm
      Re: Check-extension in QS Mikko Aarnos Fri Apr 03, 2015 6:36 pm
      Re: Check-extension in QS Sven Schüle Fri Apr 03, 2015 7:00 pm
            Re: Check-extension in QS H.G.Muller Fri Apr 03, 2015 8:34 pm
                  Re: Check-extension in QS daniel jose Fri Apr 03, 2015 9:30 pm
      Re: Check-extension in QS Shawn Chidester Fri Apr 03, 2015 8:02 pm
      Re: Check-extension in QS Lucas Braesch Fri Apr 03, 2015 11:52 pm
            Re: Check-extension in QS Lucas Braesch Sat Apr 04, 2015 12:11 am
      Re: Check-extension in QS Ferdinand Mosca Sat Apr 04, 2015 1:58 am
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