Author: Peter Berger
Date: 14:19:52 01/02/05
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Dear Chan, I was a bit reluctant to enter this discussion as you seem to have reached some honourable kind of agreement with each other to disagree already. But I am not sure this happened for good reasons, so let's start another round. I will try to not repeat things I already read (too much) , but I haven't followed the whole discussion. >My comment concerns "Test Positions" which are often given here.... >I see the Main PV scrolled... and after hours sometimes, the Computer >does not go to the "Best" move. When you have it 'locked' on the one >PV it Scrolls that Variation! You'll never know what the true eval is or what >the Best Move IS. > >Example: > >Using Multiple Lines.. >Analysis by Shredder 8: > >1. ± (1.02): 1...Qd6 2.Re1 Qb6 3.Qc2 Bd7 4.Rad1 exd5 5.exd5 Rfe8 6.Bf3 e4 7.Nxe4 >Nxe4 8.Bxe4 Qxb2 9.Qxb2 Bc3 >2. ± (1.11): 1...exd5 2.exd5 Ne8 3.f3 Nd6 4.Bf2 Bf5 5.Qa4 Qe8 6.Qb4 Qd7 7.Rfe1 >Rfc8 8.Rad1 Bf8 9.Bc5 b6 10.Qh4 >3. ± (1.26): 1...Ne8 2.Qb3 exd5 3.Nxd5 Nd6 4.f3 Be6 5.Rad1 f5 6.Qa3 Rf7 >4. +- (1.41): 1...Nxe4 2.Nxe4 exd5 3.Nc5 f5 4.f3 b6 5.Nb3 Bb7 6.Rc1 Rc8 7.Qd3 e4 >8.Qd2 Rxc1 >5. +- (1.44): 1...Qc7 2.Rc1 Bd7 3.Qb3 Rfc8 4.Rfd1 Rab8 5.Qb4 a5 6.d6 axb4 7.dxc7 >Rxc7 8.Bxe5 bxc3 9.Bxc7 > Can we please first discuss this output and what it means? This will mean I will state the obvious - please be patient with me, and not jump on me for that. You see a depth in the engine window - let's assume the engine has just finished an iteration here. It tried to find the best move for the black pieces. It found out that this is 1. ..Qd6 which will leave white up by only 1.02 of a pawn, so about a pawn up for white. Now the engine assumes that the move Qd6 is not existant and starts all over to search this depth, to produce the second line . What would be the best move then? It finds out that this is 1. ...exd5 - white would be up by 1.11 of a pawn then - that's a bit worse then what it already got for Qd6 - but it wasn't allowed to consider this move, so that's life. The engine will always search for only the best move which will be the one that provides the highest eval - its algorithms don't allow it to do anything else - it doesn't know any better. When the engine searches for the best move for the first time at a given depth ( the first line), it has no clue what eval the other moves would provide, only that it is equal or worse to what it got for Qd6. When it searches the second line it has no clue which results it will get for 3 and 4, only that it should be worse if it didn't mess up. Do we agree with each other so far ? Because if we do , I really don't get what all this discussion is about, and so it would be your task to explain now what all the computerchess guys are missing about the great options the chessprogram provides when "searching multiple lines" when it is about solving testpositions (or even worse real positions when you wouldn't know what is the best move in the first place). Let's assume in the above that 1. ...Qc7 is a brilliant move in reality that actually wins the game. Well, the engine has no clue about that. It thinks it will lose for black ( white up 1.44 pawns ) and that it sucks. Only if it is forced to forget about the best three moves , it will come up with it, and it still doesn't like it at all. What am I missing ? Peter
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