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Check extension vs LMR
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H.G.Muller



Joined: 10 Mar 2006
Posts: 21510
Location: Amsterdam

PostPost subject: Check extension vs LMR    Posted: Tue Apr 04, 2017 3:06 pm Reply to topic Reply with quote

I always adhered to the common wisdom that one should not apply LMR reductions to moves that you would extend, without giving it much thought. So when I am doing check extension, it cancels LMR.

But now I realize there is a catch, because I really used to extend the check evasions, rather than the checks. That is, when a node finds the stm in check, it increases the requested depth by 1. In the end the result is the same, the branches reach 1 ply deeper, and it does not matter where along them the extesion was awarded.

But nowadays I typically apply LMR of moves 'after the fact', that is, I first make the move, informing the daughter node it is a late move, and then leave it up to the daughter to decide about the reduction. The daughter would figure out if the stm is in check anyway, so it saves me the trouble of throwing an extra test on every move in the parent, to see if it delivers check.

But this is equivalent to exempting checking moves from LMR, and not the evasions. So some of the check evasions (in particular the King withdrawals and the interpositions) will be qualified as 'late', and will be reduced. This somehow feels wrong; I don't see any reason why these 'silent' evasions would on average have less chance to be good, or would need less depth to pove their worth as capturing the checker. Often it is the opposite: when the check was unsafe, and can be refuted by gobbling up the checker, it is usually obvious at very low depth. And if the check was safe, you are completely dependent on late moves for evasions. Normal killers or history moves are not likely to work in an in-check position.

How do other engines do this? Do they exempt checking moves from LMR, or all check evasions? Or perhaps both?
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Subject Author Date/Time
Check extension vs LMR H.G.Muller Tue Apr 04, 2017 3:06 pm
      Re: Check extension vs LMR Jon Dart Tue Apr 04, 2017 4:07 pm
      Re: Check extension vs LMR daniel jose Tue Apr 04, 2017 5:59 pm
      Re: Check extension vs LMR Robert Hyatt Thu Apr 06, 2017 6:40 pm
      Re: Check extension vs LMR Lucas Braesch Fri Apr 07, 2017 11:35 am
            Re: Check extension vs LMR H.G.Muller Fri Apr 07, 2017 5:09 pm
                  Re: Check extension vs LMR daniel jose Fri Apr 07, 2017 5:12 pm
                        Re: Check extension vs LMR H.G.Muller Sat Jun 03, 2017 11:15 am
            Re: Check extension vs LMR Nicu Ionita Fri Jun 02, 2017 7:44 am
                  Re: Check extension vs LMR Michael B Fri Jun 02, 2017 2:35 pm
                        Re: Check extension vs LMR Jonathan Rosenthal Fri Jun 02, 2017 3:03 pm
                              Re: Check extension vs LMR Michael B Fri Jun 02, 2017 3:18 pm
                                    Re: Check extension vs LMR daniel jose Fri Jun 02, 2017 6:38 pm
                              Re: Check extension vs LMR Evert Glebbeek Sat Jun 03, 2017 7:14 am
                                    Re: Check extension vs LMR Michel Van den Bergh Sat Jun 03, 2017 7:45 am
                                          Re: Check extension vs LMR Evert Glebbeek Sun Jun 04, 2017 8:37 am
                                                Re: Check extension vs LMR H.G.Muller Sun Jun 04, 2017 9:54 am
                              Re: Check extension vs LMR Jonathan Rosenthal Fri Jun 09, 2017 9:30 pm
                        Re: Check extension vs LMR Nicu Ionita Sat Jun 03, 2017 8:50 am
                        Re: Check extension vs LMR H.G.Muller Sat Jun 03, 2017 11:31 am
                              Re: Check extension vs LMR Nicu Ionita Sat Jun 03, 2017 1:21 pm
                                    Re: Check extension vs LMR H.G.Muller Sat Jun 03, 2017 1:26 pm
                                          Re: Check extension vs LMR Nicu Ionita Sat Jun 03, 2017 2:46 pm
                                    Re: Check extension vs LMR Nicu Ionita Fri Jun 16, 2017 6:06 pm
                                          Re: Check extension vs LMR H.G.Muller Fri Jun 16, 2017 6:25 pm
                                                Re: Check extension vs LMR Nicu Ionita Fri Jun 16, 2017 8:05 pm
                                                      Re: Check extension vs LMR H.G.Muller Fri Jun 16, 2017 8:49 pm
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