Author: Uri Blass
Date: 00:55:56 12/03/01
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On December 02, 2001 at 21:35:13, Gian-Carlo Pascutto wrote: <snipped> >I am faily sure that they are adjusting the alpha/beta values in >the search based on the bounds stored in the hashtable. >The technique itself is faily wellknown. The AlphaBeta in the MTD >papers has it, and I have seen several programs which applied it >too. >Basically, if during the search you get a hashtable hit which >tells you that this position is 0.5 pawns 'or more' advantage, you >raise your alpha (alpha is the value that says: a move must be >_better_ than this to become the new mainvariation) to 0.5 and prune >away everything that is less. > >This is, AFAIK, theoretically sound. The only problem is that if >the value of this branch was _exactly_ 0.5, you will also have pruned >away your mainvariation. I do not understand it and I will be happy to see an example of a tree that leads to pruning the main line. I also think that knowing the main line may be important for better order of moves so it does not make sense not to know the main line. <snipped> >For a user, it should not actually matter _at_ _all_, because one >should never trust or use anything but the first move in the mainvariation >anyway. I do not agree If I analyze a position for many hours for depth 19 and the program found an interesting sacrifice then I do not want to analyze also the position after the sacrifice for many hours to get depth 18 in order to understand the reason for the sacrifice. There are cases when correct main line can help me to understand the reason for the sacrifice(there are cases when even with a correct main line I may need a long time to understand the reason and it is better to have a list of lines that the program pondered for more than 5 seconds) Uri > >I find it redicolous that people here are complaining and calling >the Fritz 7 engine buggy (let's just not talk about the GUI ;) because >it does this, while I never saw anyone complaining about, for example, >Anmon, which displays much worse mainvariations because it uses similar >tricks. > >It's a design tradeoff. If you don't like it and want different >tradeoffs (like an >10% slower Fritz) complain to ChessBase. > >But _don't_ call it a bug, because it isn't. > >-- >GCP (not paid by ChessBase, just fed up with the reigning 'I don't understand it >so it must be broken' attitude)
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