Author: Fernando Villegas
Date: 15:48:15 01/05/00
With his usual kindness -mixed with a drop or two of subtile humor, after all the man knows me pretty well- Dgeordge Vidanovic has demanded my impressions about these Russian programs - Centaur, Mirage- as if I was knowledgeable guy of the sort capable of saying something objective about anything. I am not. The other day Christophe shot me some broadside with plenty of sarcasms precisely because my obsolete cheers for Sargon V and I must say he was damn right. I have told this many times: I NEVER play programs Vs programs, except in the rare cases when I have been asked to do so. But then, precisely because of that maybe, maybe -it is a very great MAYBE- I could say something not entirely irrelevant when the program under observation has been fitted to play humans, no more. In fact, Mirage, Centaur and CSTAL, -and perhaps also Century in a degree- are just the class of programs I love to play, or better said, with which I do not care to lose games. Humanlike in chess computer is still a debatable thing and to some here more a lot of hot air that anything else. But it is not. It is not because is not only an impression without other reason that the program launching wild attacks, but there is something in the search techniques and evaluation altogether different in them. At least in the case of CSTAL -I dared to say it many post ago- probably the algorithm is not just a variation of the current maximin technique. If you look carefully the PV’s you can see that many lines are generated not looking for the best answer to a presumed best answer in each ply, but looking at which move generates more possible bad answers for the opponent. That is, which line is more tricky. The idea is that in a real game the pressure, even if not entirely sound, is more important that teorical precision. CSTAL see chess like a fight, not like a puzzle to solve. And in a real fight you lose because sooner or later, if you are pressed, you will miss the right continuation. And if you win, you will do because the opponent made a mistake you saw and knew how to profit from it. In the case of Centaur what is human is the selection of moves. He does not seems to be interested too much in every legal move, but in a little set of relevant moves. Relevant to what? To what is happening in the board. So, mistakes are possible, but the game get a sense of direction. Besides, the probable errors that a technique like that can produce give a chance to the human side. The kick of these programs is precisely that you never feel that the computer is not prone to tactical mistakes and that every line he has seen is something like the Voice of God. Of course you can still win with programs machines-like, but only if you are so positionally skilled you can steer the bloody thing to a lost game. But for a middle age and middle level player that is not possible, of course. And which is the pleasure to test your strenght againts a mechanical lever? Or to win because you previously disabled half of his strenght? I prefer to lose to Fritz in full gear than to win him because I setted it to play like a 1600 player. Now probably you ask yourself: where I can get Centaur...? But in the meantime you solve that puzzle, this is what author say about his technique: "This window shows the Centaur thinking process. To choose the next move Centaur first overlooks all possible moves and obtains the distributions of probable gain or loss for each of them, then the move having the maximal more probable estimation gains a vote. Centaur makes attempts to disprove this move. During this procedure the move can gain more vote or be rejected, this causes selection of another move and so forth. This algorithm is more intimate with a human thinking then a tedious speed exhaust of the others' chess programs. When any move obtains first vote, there appears the move string and the color bar showing the probability of gain obtained by this move. The gains or losses (if negative) are shown in the 'pawn' units, that is gain the number of pawns. The blue slide bar shows the range in which the gain (or loss) lay with the probability of 99% at the current state of approximations. The red bar contains the gain with the probability of 90%. The vertical line marks the maximum of probability. When analyzing the moves, the spread in possible gains is getting less, and Centaur approaches a decision. After all, Centaur makes the move obtaining more votes. The bar height shows the comparative number of votes. Naturally Centaur continues thinking during your turn, and you can use its analyses as a hint. The Thinking window takes the same place together with the Open book window because of they never used simultaneously. When they both are open, the Thinking window is visible only if the library is exhausted..."
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