Author: Peter Kappler
Date: 11:07:00 02/16/06
Go up one level in this thread
>>>>> >>>>>In practice this doesn't happen. The real problem is that by round 6, the >>>>>winner is pretty certain, although three games against weaker opponents are >>>>>left, and there the luck factor often lurks behind a pawn and jumps out to >>>>>present a surprise and knock one of the top players off. >>>>> >>>> >>>>I have to believe that you're half-kidding here. Surely you don't believe that >>>> adding 3 more rounds increases the variance of the final result? >>>> >>>>-Peter >>>> >>> >>>Yes, it absolutely does. Simple example: 4 strong programs, 12 weak ones. >>>after round 1, you have 8 with 1, 8 with 0, the 8 with 1 include the top 4. >>>After two rounds, the top four have two, the bottom four have 0, and the rest >>>have 1 (assuming no draws). after 3 more rounds the top four have played. What >>>now for those other 4 rounds? Other programs? With the luck factor increasing >>>variance? >>> >> >> >>What is this "luck factor"??? > >It is something seen in _every_ tournament played. A weaker program stumbles >into a winning position, either being lucky with the book, or just lucky in >making a move it didn't understand was good, but which turned out to be good >many moves later. > >I can refer you to the game Nuchess - Cray Blitz at the 1984 ACM event. We >played a horrible-looking Nb8 move. But it later let us trade off all the >pieces and win a pawn-race because white simply didn't understand unstoppable >pawns. But had black not played that one ugly move, for the wrong reason, white >would have won handily. > >Every tournament has a luck factor thrown in. Even in my human chess games, I >occasionally stumble into something I had not forseen, and win because of it. > > >> >>If one of the strong programs loses or draws against one of the weak programs, >>that's not luck - it's a signal that the program might not be as strong as you >>thought. > > >It can be luck plain and simply. You have three moves to choose between, at the >depth you are searching, all three have _identical_ scores even though one will >later turn out to be winning, one will turn out to be losing, and one will turn >out to be pretty "equal". What determines which move your search chooses? Luck >of move ordering at the root. Since the first move with equal scores will be >chosen by alpha/beta. I can play a move that is lucky in that it wins even >though I don't know it at the time, I can play a move that is unlucky in that it >loses later in the game. > >That's luck, since it is based on random choice rather than any sort of chess >knowledge or skill. > Sure, these things can happen, but it is the exception rather than the rule. Most chess games are not decided by luck, and this is why playing more rounds in a tournament definitely reduces the variance of the result. > > >> >>It seems obvious to me that increasing the number of rounds always reduces the >>variance of the final tournament standing, regardless of the distribution of the >>participants' ratings. >> > >Seems to me that if you look at events starting at round 6 and on, nothing much >changes since the leaders have all played because of the Swiss pairing rules. >But lower-rated programs still move up and down and a few collect right below >the leaders. If all programs were pretty equal, extra rounds would not really >make that much of a difference. But they are not equal, and strong vs weak in >late rounds doesn't do a thing for overall result confidence. > Those "extra" rounds have decided the winner in at least a few of the CCT tournaments. -Peter
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