Author: Bas Hamstra
Date: 14:12:48 04/13/02
Go up one level in this thread
I have a theory about 1 In an earlier program, I uses aspiration search, a was plagued by massive false fail highs and lows. That's why I abandoned the use of aspiration windows. Currently I still use no aspiration window, at the root I search the first move with full window, and the rest with a nullwindow. At a fail high, I simply research with <alpha, beta>. So in theory I should still suffer from false fail highs. I just did a quick test. I see them, but *rarely*, only a very small fraction of what I used to see. One important difference is that this program does qchecks, the previous program did not. Frans does qchecks, no false FH's. Vincent does qchecks, no false FH's. Best regards, Bas. BTW: can anyone backup with some data that the use of an aspiration window is good? On April 12, 2002 at 15:08:51, Gian-Carlo Pascutto wrote: >To start off, I want you all to take a quick look at the >two following logs. > >The first is from Fritz 7, the second from Shredder 6. > >------------------------------------------------------------------ >26.Rb7+ Kc6 27.R7xb4 Rxb4 28.Bxb4 Kd5 29.Rxd3+ Kc4 30.Re3 Rxe3 > +- (1.78) Depth: 6/17 00:00:00 21kN >26.Rb7+ Kc6 27.R7xb4 Rxb4 28.Bxb4 Kd5 29.Rxd3+ Kc4 30.Re3 Rxe3 31.fxe3 Kxb4 > +- (1.78) Depth: 7/21 00:00:00 46kN >26.Rxf7! > +- (1.81) Depth: 7/21 00:00:01 74kN >26.Rxf7 Re2 27.Rb7+ Kc5 28.Bxb4+ Kc6 29.Rxg7 d2 > +- (1.84) Depth: 7/21 00:00:01 82kN >26.Bxb4! > +- (1.88) Depth: 7/22 00:00:01 113kN >26.Bxb4! > +- (2.03) Depth: 7/22 00:00:01 123kN >26.Bxb4 Rxb4 27.Rb7+ Kc6 28.R7xb4 Re1+ 29.Ka2 d2 > +- (2.16) Depth: 7/22 00:00:01 140kN >26.Bxb4-- > +- (1.88) Depth: 8/22 00:00:02 158kN >26.Bxb4 Rxb4 27.Rb7+ Ka5 28.Ra3+ Ra4 29.Ra7+ Kb6 30.R3xa4 > +- (1.84) Depth: 8/23 00:00:03 196kN >26.Rxf7! > +- (1.88) Depth: 8/23 00:00:03 247kN >26.Rxf7! > +- (2.03) Depth: 8/23 00:00:03 273kN >26.Rxf7 Re2 27.Rb7+ Kc6 28.R7xb4 Rd5 29.Rb6+ Kc7 30.Rb7+ Kd6 31.R3b6+ > +- (2.16) Depth: 8/23 00:00:03 315kN >------------------------------------------------------------------ > 2.00 0:00 +0.28 6.Ne5 O-O (141) 28.2 > 2.00 0:00 +0.30++ 6.Qd3 Nc8 (386) 38.6 > 2.00 0:00 +0.31 6.Qd3 Nbc6 (562) 51.0 > 2.00 0:00 +0.34++ 6.a3 Bxc3+ 7.bxc3 Nf5 (878) 10.8 > 2.00 0:00 +0.37 6.a3 Bxc3+ 7.bxc3 O-O (960) 11.7 > 3.00 0:00 +0.31 6.a3 Bxc3+ 7.bxc3 O-O 8.Qd3 (1.573) 17.2 > 4.00 0:00 +0.17 6.a3 Bxc3+ 7.bxc3 O-O 8.Qd3 d5 9.cxd5 Bxd5 (3.858) 23.6 > 4.00 0:00 +0.18++ 6.Qd3 Bxc3+ 7.bxc3 Bc8 (5.421) 26.9 > 4.00 0:00 +0.18 6.Qd3 O-O 7.Bxe7 Qxe7 8.Ng1 (8.727) 32.9 > 5.00 0:00 +0.10 6.Qd3 O-O 7.a3 Bxc3+ 8.bxc3 f6 9.Bf4 (20.072) 44.1 > 5.00 0:00 +0.11++ 6.a3 Bxc3+ 7.bxc3 Bxf3 8.gxf3 d5 9.cxd5 Nxd5 (20.507) 44.6 > 5.00 0:00 +0.11 6.a3 Bxc3+ 7.bxc3 O-O 8.Rc1 d5 9.cxd5 exd5 (21.549) 44.0 > 5.00 0:00 +0.12++ 6.Qb3 Bxc3+ 7.Qxc3 Bxf3 8.Qxf3 Nd5 9.Bxd8 Kxd8 (26.941) >46.2 > 5.00 0:00 +0.12 6.Qb3 Bxc3+ 7.Qxc3 O-O 8.Bf4 Nbc6 9.Ng1 (30.312) 47.2 > 6.00 0:01 -0.05 6.Qb3 Na6 7.a3 Bxc3+ 8.Qxc3 f6 9.Bf4 O-O (70.114) 55.3 > 6.00 0:01 -0.04++ 6.Qd3 O-O (73.372) 55.5 > 6.00 0:01 -0.03 6.Qd3 O-O 7.a3 Bxc3+ 8.bxc3 Nbc6 9.c5 (85.695) 55.7 > 6.00 0:01 -0.02++ 6.Bxe7 Bxe7 7.e4 Na6 8.Ne5 (110.658) 57.2 > 6.00 0:02 +0.01 6.Bxe7 Bxe7 7.e3 c5 8.Be2 cxd4 9.Qxd4 O-O (119.562) 57.3 > 6.00 0:02 +0.02++ 6.e3 Bxc3+ 7.bxc3 Bxf3 8.gxf3 Nbc6 9.a3 (130.227) 57.7 > 6.00 0:02 +0.15 6.e3 Bxc3+ 7.bxc3 f6 8.Bf4 e5 9.dxe5 O-O 10.exf6 Rxf6 >(141.644) 58.7 > 7.01 0:03 +0.18 6.e3 Bxc3+ 7.bxc3 f6 8.Bf4 e5 9.dxe5 O-O 10.Bd3 (183.860) >60.2 > 8.01 0:05 +0.22 6.e3 Bxc3+ 7.bxc3 f6 8.Bf4 e5 9.dxe5 O-O 10.Bd3 Nbc6 >11.exf6 (330.335) 62.6 >------------------------------------------------------------------ > >As far as we know, these programs are based on PVS frameworks. >(When I'm talking about fail high, I mean on a different than >the first move, not the aspiration window thing) > >So, what's wrong with the picture? > >-> These programs have _no_ false-fail highs! <- > >I spent some time looking at output from Fritz >and Shredder, and I saw zip, nada, niente, nothing. > >Of course, if your program doesn't print the initial >fail high, you wont see false fail highs either, but >then you always have full reliable mainvariations to go >with them. If you look above, you see that this is not >the case. So I presume what they print out is the initial >fail high. > >How is this possible? > >Even worse, there are two other things that are fundamentally >strange: > >1) Fritz seems to use a very (0.05-0.15) small window when >doing the research on the FH move, and opens it up gradually. > >2) Shredder has _variations_ to go with the initial fail-highs > >I thought about (1), and my initial guess was that they do >the small window researches to check whether the move is a >real fail high, be able to reject it without doing an open-window >research, and save some time because of the smaller window. > >That can't be it. If a move would be, say, only 0.03 better, >you'd fail low and have to do another research to figure out >if the move is a real fail high or not. Moreover, the moves >that fail high the first time always end up being the PV. >Essentially, Fritz has no false fail highs. I'm clueless as >to what's happening here. > >So I moved to (2). Something to note is that these variations >aren't always complete nor do they always make sense. They're >likely coming out of the hashtable. I can get my thing to >have similar behaviour by storing best moves even on fail-lows. >Although this is essentially unreliable, the first 2-3 moves >usually are correct, and this is consistent with what I see >in Shredder. So perhaps this little mistery is partly solved. >However, we also see that Shredder _never_ has false fail >highs. > >Perhaps these program have a search so stable that they simply >don't happen? Sounds unlikely doesn't it? > >Do they have a trick which they use to determine whether a >fail high is real or not? I don't see how this could be >possible. > >I have another thought, which may or may not be related to >these issues. > >Why don't MTD(n,f) searchers have trouble with this? If the >PVS can have a fail high/fail low sequence, couldn't this >happen with MTD(n,f) as well? As far as I see, the result >would be that the MTD quits (it has converged, after all) >and ends up with the move that corresponds to the false-fail >high one in PVS. These are often blunders. Why doesn't this >happen? > >-- >GCP
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