Author: Amir Ban
Date: 15:50:46 11/16/98
Go up one level in this thread
On November 16, 1998 at 17:56:09, Robert Hyatt wrote: >On November 16, 1998 at 16:53:28, Amir Ban wrote: > >>On November 16, 1998 at 14:36:32, Robert Hyatt wrote: >> >>>On November 16, 1998 at 12:09:33, Amir Ban wrote: >>> >>>>> >>>> >>>>I don't think so. This one is not a "nonsense" PV. It's genuine and needs an >>>>explanation. >>>> >>>>Amir >>> >>>Here's a very precise question for you: Have you *ever* had Junior analyzing >>>games where others could see it's output? An example: I often have Crafty >>>give online analysis on ICC when GM's are playing in major tournaments. And >>>in *every* game, someone will do this: Take a PV returned by a 13 ply search, >>>play the moves on a "scratch" board, then say "hey all you guys that were >>>amazed that Crafty had predicted all of the last 30 moves but one, look at >>>this position after it's analysis." And invariable there will be some funny >>>stuff at the end of the PV that produces a position that is quite questionable >>>when looked at in that light. >>> >>>So, the point is, then, is it really important to look at moves further down >>>the PV and try to justify *them* as well? Or is the move played at the root >>>the place where we want the most accuracy? I'd *love* to do 13 ply searches >>>and produce 16 move PV's where every move was of GM caliber. But I know that >>>the root move will be *very* good. The second move a little worse because it >>>is a 12 ply move... the third move a little worse still... etc... I often >>>see oddball moves near the end of a PV, when the goal is to simply prevent some >>>"threat" that I analyze from happening (IE Qa2 to prevent your playing Rb2, even >>>though Rb2 is totally unimportant while Qa2 puts the queen in a horrible >>>position.) I fix what I can, but I still see this. In fact, I see this in >>>*all* programs that I watch where the operator will cut/paste analysis and send >>>it to ICC... >>> >>>I'm much less worried about what's happening at the *end* of DB's PV's than >>>I am interested in what is happening at the *front*. I'm sure you must have >>>seen positions where there was a sequence in the PV that goes like this: >>> >>>1. Nc3 Bf2+ Kh1 or 1. Kh1 Bf2 Nc3. Same position, right? Not quite. That >>>+ drives the PV one move deeper along that path, so if there is something I can >>>do deep in the tree I don't move my king, knowing he won't check to extend my >>>search so that I can see the result, or if it is something bad, I'll move my >>>king so he can't check me and drive the search deep enough where I see the bad >>>thing. Horizon gets us all from time to time, still. Lots of reasons to >>>explain an unexpected queen move. From horizon, to eval quirk (defending >>>against a useless threat) to a parallel search anomaly to a hashing anomaly to >>>an outright bug. But I don't see why "it needs an explanation." Maybe we are >>>curious and we have to figure out why... but I certainly don't intend to spend >>>the rest of my days explaining every odd thing my program does... otherwise I >>>won't ever get anything else done, because it does *lots* of odd things still. >> >> >>I am afraid that once again you plunge into a long and irrelevant monologue >>because you do not take a few seconds to check what it is I'm asking and why. >> >>Amir > > >No I didn't... I assumed the following, first: > >1. that you had looked at the position after Qxc3... looking at that I >definitely like white... white didn't "abandon the c3 pawn" it is threatening >to take axb5 and end up with two connected passed pawns, the queen on the 7th, >the rooks behind those pawns, etc... so white is not hurting there and when >I search from that position I get a score of +1.5, which may well be the >reason DB played down that line, although when I search from the original >position I don't get that big a score. > >2. I assumed that you understand that the DB chess processors do *not* produce >a PV. Which means there PV ends where the chess processors take over, which is >the last 4 plies of full-width search plus the capture search and whatever they >do about checks and evading the checks out there. So just because the PV ends >with Qxc3 does *not* mean that's where they stopped and did a static eval. > >So, in light of those explanations, I assumed you were more concerned about the >move Qa7 at the end of the PV, and the fact that it seems like an odd move. It >doesn't seem odd to me, but if it does to you, there are several different >reasons why moves near the end might seem like something you wouldn't play. In >this case, Qa7 seems perfectly natural. I do assume that before you would make >a remark like "Qa7 needs an explanation" that you ran that position thru your >program? I did it to mine... and here's what I get for the scores of the >two best moves: > >Qf2: > 12 2:07 0.53 5. Qf2 axb5 6. Qe1 Qxf5 7. Bg4 Qe5 > 8. Be6+ Kh7 9. Qxe5 Bxe5 10. Ra3 Rd6 > 11. Kf2 Kg6 > >and Qa7 which is always at the top of my move list right below Qf2: > > 12 2:41 0.33 5. Qa7 axb5 6. Ra6 Re8 7. Rd1 Rbd8 > 8. Ra3 Qxf5 9. Qb6 Qd7 10. Ra7 Rb8 > 11. Rxd7 Rxb6 > > >When I saw that the scores different by .2 pawns, I apparently assumed you >had done something you had not. > >Summary: > >Qa7 is *not* unusual since Crafty ranks it as the second best move thru 12 >plies where I stopped this. Near the end of a PV *anything* can happen. And >finally, DB doesn't show *all* the PV *ever* because of the hardware chess >processors not keeping up with this... And I'd hope that point 3 is common >knowledge since it was known back in the days of Belle as well. Ken did >2 plies in software and the rest in hardware and only had 3 move PV's unless >the software extended... because the hardware just returns a "best move" and >"best score for that move." > >Is there anything *else* about the PV you had that seems odd? The main thing >I can't see is the extensions (singular) that DB does... If this position is >forced (or can be forced by white) from the original axb5 then there is *no* >mystery why they changed from Qb6... because the score is *higher* after >following that PV and then searching deeper to compensate for their speed. > >Mystery closed on that point? No. I have no idea how so much confusion is possible, but none of what you say makes sense to me in this position. Qf2 is not even possible here, the queen is on a6. You must have the wrong position. Here it is again, with the PV: [Event "?"] [Site "?"] [Date "?"] [Round "2"] [White "Deep Blue"] [Black "Garry Kasparov"] [Result "1-0"] [ECO "?"] [FEN "r1r1q1k1/6p1/p2b1p1p/1p1PpP2/PPp5/2P4P/R1B2QP1/R5K1 W - - "] 36. Qb6 Qe7 37. axb5 Rab8 38. Qxa6 e4 39. Bxe4 Qe5 40. Bf3 Rd8 41. Qa7 Qxc3 42. Bh5 * We are discussing 41.Qa7. Amir
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