Author: Serge Desmarais
Date: 17:49:56 09/09/98
Go up one level in this thread
On September 09, 1998 at 20:15:22, Alessio Iacovoni wrote: >On September 09, 1998 at 19:15:25, Serge Desmarais wrote: [Snip] >> >> >> Well, I admit it wasn't as clear as I wanted it to. But it is not too easy to >>describe/explain either (or maybe I am one guy that makes things look more >>complicated than it should?). And maybe the fact that I own Fritz 5, makes me >>take some things for granted? >> >> Okay! Let's go back to my opening tree made from 100,000 games. I said that >>1.e4 had been played in 60,000 games, so 60% of the time. So, with only this >>data, Fritz could decide to give it a 60% chances of being played. At base, I >>suppose it generates a random move (like running a dice) and 60% of the possible >>moves that could be generated would make it play 1.e4. This is a basic. Now, how >>is it "balanced"/adjusted? Suppose that in the games imported, the scores were >>that the White side got 55% of the possible points (assuming 1 point is for a >>win, and 0.5 point for a draw) : so of the possible 60,000 points (like in a >>60,000 games match!) White got 33,000 points and Black 27,000. (Again these >>round and unrealistic numbers are fictitious, created just for the example). >>Now, suppose the second most popular first move is 1.d4 which was played 30,000 >>times (30%) BUT earned White an incredible 65% of the possible points! So, over >>all, that move seems very promising. So, instead of having 30% of picking that >>move, Fritz could increase the percentage to, say, 36% while decreasing the one >>of 1.e4 to, say, 52%. (Instead of using the word "balance", maybe I should have >>said ADJUST?). >> >> >> Now, tell me, if you had the choice (as White) between playing 2 moves : one >>played by Kasparov (rated over 2800) and one played by a 1900 player, which one >>would you favor? A lot of people would say Kasparov's one! Of course, >>OBJECTIVELY the move of the unknown 1900 player COULD be better. But globally, >>we could assume that Kasparov would usually play better moves than most players, >>since he had better results. That is exactly what Fritz does to further adjust >>the probability of its book's moves of being played! Looking at the average >>rating of the players for all the moves, suppose 1.e4 was played by people >>averaging 2560, while 1.d4 was played by people averaging 2222. Then because of >>that, Fritz could decrease the probability of 1.d4 to, say, 23%, while >>increasing the chances of 1.e4 to 65%. >> >> >> Now, this description could give the impression that all these steps are done >>in that order and one after the other. I think they are all variables of a >>mathematical formula and everything is adjusted in a fraction of a second. >> >> >> >> >> Now, about the "refining". When Fritz plays a move in one of its own game >>(picking the moves according randomly, based on their respective percentage at >>each position), it will then adjust the percentage based on the game score. If >>it is a win, it will put an asterisk near 1.e4 (the move that was played) to >>show that it adjusted the value based on the experience it had with this move. >>The adjustment range from -125 to +125. For a win, 1.e4 could get a, say, +3. If >>it was, say, a Ruy Lopez and it stayed in its book for the first 22 moves, the >>last one played (the 22nd) would get a bigger adjustment, maybe something like >>+43. If you go back from that 22nd move and back to the first, uou would notice >>that the closer you go to the starting position, the smaller the adjustments. >>Losing or drawing means a negative adjustment, the losts being worse and so a >>bigger adjustment. >> >> "Sensible" was used because of one of its French meanings : perceptible, >>obvious, in a drastic way. I saw that it has by no means the same meaning in >>English! >> >> >> >> Now you asked me if the opponent hadn't a word to say about the openings >>chosen. Of course it has! If Fritz plays a lot of different opponents and/or >>opponents which vary their openings and defense a lot, it will endup with >>"favorite lines" against the Sicilian Najdorf, Paulsen and all, against the >>various defenses in the Ruy Lopez and will also sets preferences for its >>defenses against the English, Queen pawn, King pawn openings and others, and >>agaisnt subvariations too... As soon as it encounters a book positions for which >>its book contains more than one choice of moves, it will pick one according to >>what I explained above and further adjust its score based on the result of the >>game(s) in which it played it, according to the score(s) it got with it! So, it >>will NEVER repeat moves/games that lead/ended to/as draws or losses and ALWAYS >>repeat moves leading to wins, as long as it wins with it. >> >> This way, and with that drastic learning, it is able to adapt very quickly to >>another computer/program or even human and learn to avoid >>lines/openings/defenses that lead Fritz into trouble (were to easy to >>play/understand for the opponent)! If you look at the previous SSDF list, you'll >>notice that the match between Fritz P200MMX against Genius 5 P200MMX was tied 9 >>to 9 after 18 games played (at 40 moves in 2 hours), but then Fritz outplayed >>its opponent 20.5 to 9.5 in the next 30 games! What happened, do you think? It >>was repeating the openings leading to wins and avoiding positions in which it >>was not able to crack Genius or that Genius was playing better than itself. But >>Genius continued repeating openings that lead to lost games... >> >> >> >> >> Now there was something interesting you made me think about. Since the >>opening books of every programs/computers are made from human games/lines, it >>would be interesting to see a program playing with a book made from its own >>calculations/preferred moves? Komputer Korner suggested, a few months ago, to >>altogether (we who own chess programs) to reexamine all the existing opening >>lines with various programs and only keep the good moves (according to >>computers) and add new lines entirely created by computers. Of course, every >>participant would pick a different opening. We could let the program calculate >>over a position/examine it for long minutes, and sometimes hours? Ending up with >>a "perfect" opening book or at least one that could better fit computer's style? >> >> >> >>Serge Desmarais > >Question. I don't have Fritz so I don't know the answer. Now, that I remember of >usually chess programs tend to avoid very closed openings.. even if in "human" >tournaments they would lead to a loss. So.. if I answer f5 to d4 would the >computer follow up the line to the very closed stonewall variation (which in the >end are considered to be anyway favourable to white?), if not on what base would >it avoid the very closed variation, eventually preferring the more open ones, if >the opening book is not tuned at all for computers? It would not avoid the line at first. If the moves were played often (% higher than those of of the other book moves for these positions) and the GMs who played these had a high rating AND the score was in White's favor, it is probable that it will play the line. Now, as I said above, it puts probabilities of being played for every move. Though it would NEVER play a move that is given a probability of 0% of being played, based on the factors I mentionned, there is always a chance that it plays a move which has between 1 and 99% of being picked, as long as it is ABOVE 0%! It will ALWAYS play THE move that has 100%. Now, if it plays the Stonewall variation and it wins, it will always play it there after, as long as it wins as White. If you manage to draw as Black on the first game, it will avoid it after, though. So, no, there are no specific lines/kind of positions that it tries to avoid. In the default book, for example, I imported positions from several thousand games with the Caro-Kann Defense and for a while, it started to play it (against other computers). Until a few draws occured, after which, it reduced its percentage from 100% to above 20%! Importing new games in which certain moves were played tends to increase the chance for these moves to be played. Also, if you like playing the Dutch Defense and would like to train in playing the Stonewall variation, you can still manually increse the adjustment values for the moves leading to it (setting them at +125 and the other moves/lines which avoid it to -125. Or you could setup positions and start playing from there. You could also select specific games in a PGN/CBH/CBF database and import their moves (say, the first 20-30 moves) into your opening tree. Only problem could be that these games could contain blunders or mistakes in the first 30 moves (even losing ones!) that the program would play (ONLY ONCE if it loses, but ALWAYS if it wins with it!). Serge Desmarais
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