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SEE on non-capture moves in main search
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Tord Romstad



Joined: 08 Mar 2006
Posts: 1750
Location: Oslo, Norway
PostPost subject: Re: SEE on non-capture moves in main search    Posted: Thu Mar 29, 2007 12:39 pm Reply to topic Reply with quote
hgm wrote:
Well, my gut reaction to this is that it would not matter, exactly because there are so few PV nodes. Are the sub-trees from PV nodes really that much bigger then from all nodes? I would guess that this matters only a factor ~2.

The sub-trees below PV nodes are certainly a lot bigger, but exactly how much depends on the program. Many programs extend more and prune and reduce less in PV nodes, for these programs the factor will obviously be bigger.

In any case, the difference in tree size between a PV node and a non-PV is non-trivial, especially when move ordering is poor at the PV node. At a PV node, every time a move after the first returns a score above alpha, you have to do an expensive re-search with a big window. If the best move changes several times at the same PV node, it takes a lot of time to finish the node.

You can see this most clearly at the root of the tree. Consider how much longer it takes to complete an iteration when the best move changes multiple times. Exactly the same thing can happen at internal PV nodes, except that you don't see it as easily. The consequences can be quite bad, especially for PV nodes with a big remaining depth.

Quote:
Since all my engines rely on an advanced IID scheme, I am probably not very sensitive to this effect anyway. By the time any significant depth is reached, the earlier iterations will have picked out the best move fairly reliably, and once a move scores above alpha, I keep it from then on in the early part of my move list.


But what happens if the score of the first move at a PV node suddenly drops by a big amount compared to the previous iterations? I think it might be a good idea to look for a good way to select a promising second move to search. One approach I have considered (but not yet tested) is to do an IID search with the first move removed from the move list at PV nodes where the score of the old best move drops a lot compared to the previous iteration.

Tord
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Subject Author Date/Time
SEE on non-capture moves in main search Gary Wed Mar 28, 2007 11:25 pm
      Re: SEE on non-capture moves in main search Robert Hyatt Thu Mar 29, 2007 1:17 am
            Re: SEE on non-capture moves in main search Tord Romstad Thu Mar 29, 2007 10:03 am
                  Re: SEE on non-capture moves in main search ed Thu Mar 29, 2007 1:34 pm
                        Re: SEE on non-capture moves in main search Sam Hamilton Fri Mar 30, 2007 12:07 am
                        Re: SEE on non-capture moves in main search Tord Romstad Fri Mar 30, 2007 11:46 am
                  Re: SEE on non-capture moves in main search Robert Hyatt Thu Mar 29, 2007 9:35 pm
                        Re: SEE on non-capture moves in main search H.G.Muller Thu Mar 29, 2007 10:27 pm
                              Re: SEE on non-capture moves in main search Robert Hyatt Fri Mar 30, 2007 12:05 am
                                    Re: SEE on non-capture moves in main search H.G.Muller Fri Mar 30, 2007 6:50 am
                                          Re: SEE on non-capture moves in main search Robert Hyatt Fri Mar 30, 2007 9:27 pm
                                                Re: SEE on non-capture moves in main search Tord Romstad Fri Mar 30, 2007 10:29 pm
                                                      Re: SEE on non-capture moves in main search Robert Hyatt Sun Apr 01, 2007 1:51 am
                                                            Re: SEE on non-capture moves in main search Tord Romstad Sun Apr 01, 2007 7:54 am
                                                                  Re: SEE on non-capture moves in main search Robert Hyatt Mon Apr 02, 2007 1:57 am
                                                            Re: SEE on non-capture moves in main search H.G.Muller Sun Apr 01, 2007 10:22 am
                                                                  Re: SEE on non-capture moves in main search Robert Hyatt Mon Apr 02, 2007 2:05 am
                                                                        Re: SEE on non-capture moves in main search H.G.Muller Mon Apr 02, 2007 12:31 pm
                                                                              Re: SEE on non-capture moves in main search Robert Hyatt Mon Apr 02, 2007 3:56 pm
                                                                                    Re: SEE on non-capture moves in main search Steven Edwards Mon Apr 02, 2007 4:44 pm
                                                                                          Re: SEE on non-capture moves in main search H.G.Muller Mon Apr 02, 2007 4:59 pm
                                                                                          Re: SEE on non-capture moves in main search Robert Hyatt Mon Apr 02, 2007 6:44 pm
                                                                                          Re: SEE on non-capture moves in main search Robert Hyatt Mon Apr 02, 2007 6:40 pm
                                                                                    Re: SEE on non-capture moves in main search H.G.Muller Mon Apr 02, 2007 4:53 pm
                                                Re: SEE on non-capture moves in main search H.G.Muller Sat Mar 31, 2007 8:38 am
                                                      Re: SEE on non-capture moves in main search Robert Hyatt Sun Apr 01, 2007 1:59 am
                                                            Re: SEE on non-capture moves in main search Tord Romstad Sun Apr 01, 2007 7:58 am
                                                                  Re: SEE on non-capture moves in main search Robert Hyatt Mon Apr 02, 2007 3:57 pm
                                                                  Re: SEE on non-capture moves in main search Peter Fendrich Mon Apr 02, 2007 5:19 pm
                                                                        Re: SEE on non-capture moves in main search Robert Hyatt Mon Apr 02, 2007 6:46 pm
                                                                        Re: SEE on non-capture moves in main search Tord Romstad Mon Apr 02, 2007 6:51 pm
                                                                              Re: SEE on non-capture moves in main search Peter Fendrich Mon Apr 02, 2007 7:53 pm
                                                                                    Re: SEE on non-capture moves in main search H.G.Muller Mon Apr 02, 2007 9:01 pm
                                                                                          Re: SEE on non-capture moves in main search Peter Fendrich Mon Apr 02, 2007 9:30 pm
                                                                                          Re: SEE on non-capture moves in main search H.G.Muller Tue Apr 03, 2007 8:46 am
                                                                                          Re: SEE on non-capture moves in main search Peter Fendrich Tue Apr 03, 2007 10:29 am
                                                                                          Re: SEE on non-capture moves in main search Robert Hyatt Tue Apr 03, 2007 9:23 pm
                                                                                          Re: SEE on non-capture moves in main search Tord Romstad Wed Apr 04, 2007 2:38 pm
                                                                                          Re: SEE on non-capture moves in main search Peter Fendrich Wed Apr 04, 2007 7:49 pm
                                                                                          Re: SEE on non-capture moves in main search Tony Tue Apr 03, 2007 10:54 am
                                                                                          Re: SEE on non-capture moves in main search Robert Hyatt Tue Apr 03, 2007 9:24 pm
                                                                                          Re: SEE on non-capture moves in main search H.G.Muller Tue Apr 03, 2007 9:29 pm
                                    Re: SEE on non-capture moves in main search Tord Romstad Fri Mar 30, 2007 11:40 am
                              Re: SEE on non-capture moves in main search Tord Romstad Fri Mar 30, 2007 11:54 am
                                    Re: SEE on non-capture moves in main search H.G.Muller Fri Mar 30, 2007 1:28 pm
                                          Re: SEE on non-capture moves in main search H.G.Muller Fri Mar 30, 2007 4:41 pm
                        Re: SEE on non-capture moves in main search Tord Romstad Fri Mar 30, 2007 11:30 am
                              Re: SEE on non-capture moves in main search Uri Blass Fri Mar 30, 2007 11:50 am
                                    Re: SEE on non-capture moves in main search Tord Romstad Fri Mar 30, 2007 10:32 pm
                              Re: SEE on non-capture moves in main search H.G.Muller Fri Mar 30, 2007 12:16 pm
                              Re: SEE on non-capture moves in main search Robert Hyatt Fri Mar 30, 2007 9:32 pm
                                    Re: SEE on non-capture moves in main search Tord Romstad Fri Mar 30, 2007 10:00 pm
      Re: SEE on non-capture moves in main search Mark Lefler Thu Mar 29, 2007 6:30 am
      Re: SEE on non-capture moves in main search H.G.Muller Thu Mar 29, 2007 9:28 am
            Re: SEE on non-capture moves in main search Tord Romstad Thu Mar 29, 2007 10:13 am
                  Re: SEE on non-capture moves in main search H.G.Muller Thu Mar 29, 2007 12:03 pm
                        Re: SEE on non-capture moves in main search Tord Romstad Thu Mar 29, 2007 12:39 pm
                              Re: SEE on non-capture moves in main search H.G.Muller Thu Mar 29, 2007 2:15 pm
                                    Re: SEE on non-capture moves in main search Zach Wegner Thu Mar 29, 2007 9:10 pm
                  Re: SEE on non-capture moves in main search Steven Edwards Thu Mar 29, 2007 2:18 pm
                  Re: SEE on non-capture moves in main search Rob Sun Apr 01, 2007 6:01 pm
      Re: SEE on non-capture moves in main search Gary Sun Apr 01, 2007 8:26 am
      Re: SEE on non-capture moves in main search Markoff Thu Apr 05, 2007 11:25 pm
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