Author: Robert Hyatt
Date: 13:34:35 10/23/01
Go up one level in this thread
On October 23, 2001 at 13:05:49, Gordon Rattray wrote: >On October 23, 2001 at 11:37:07, Robert Hyatt wrote: > >>On October 23, 2001 at 10:19:53, Gordon Rattray wrote: >> >>>On October 23, 2001 at 09:58:52, Robert Hyatt wrote: >>> >>>>On October 23, 2001 at 08:56:18, Gordon Rattray wrote: >>>> >>>>>Suppose that during the analysis of a position, a chess engine shows evaluations >>>>>similar to this: >>>>> >>>>>depth 7: Qe1 eval: 0.58 >>>>>depth 8: Qe1 eval: 0.42 >>>>>depth 9: Qe1 eval: 0.39 >>>>>depth 10: Qe1 eval: 0.33 >>>>> >>>>>i.e. as the depth increases, the move choice stays the same, and the evaluation >>>>>is slowly but consistently decreasing. >>>>> >>>>>I release that in general the next evaluation could be anything, but I am right >>>>>in thinking that the probability of it decreasing further is higher than normal? >>>>> Or to take it to extremes, I think the above is more likely to decrease further >>>>>than the following: >>>>> >>>>>depth 7: Qe1 eval: 0.33 >>>>>depth 8: Qe1 eval: 0.39 >>>>>depth 9: Qe1 eval: 0.42 >>>>>depth 10: Qe1 eval: 0.58 >>>>> >>>>>Did each line involve a "fail low"? Or am I getting my terms mixed up? >>>>> >>>>>Do chess programs take account of the above and, e.g., are more likely to search >>>>>further before moving? >>>>> >>>>>Gordon >>>> >>>> >>>>That generally suggests that there is a horizon-effect happening, and that >>>>eventually the best move will be bad enough that a new best move will be >>>>found. >>> >>>Thanks, that confirms my thinking. One position in which I seen the effect >>>involed White grabbing a pawn at the expense of uncoordinated pieces. So, the >>>term "horizon effect" seems applicable. >>> >>>> >>>>But searchng until you find it is not possible in a timed game, for obvious >>>>reasons... >>> >>>Sure, but can't the timing code take this into some consideration? For example, >>>if the next iteration is estimated to take too much time, but only just over the >>>allowable period, would it be worthwhile paying that bit extra? Alternatively, >>>can increasing evaluations be used as a factor for moving quicker? I'm not >>>suggesting that there wouldn't be other factors in either case. >>> >>> >>>Gordon >> >>That is the trivial case. But suppose the _last_ iteration is only .1 worse >>than the previous iteration. And suppose the next iteration will take 20 >>minutes (estimated) to search? And if that one is again .1 worse, the next >>will take probably an hour... > > >Agreed. > >It's the probability of avoiding a possible horizon effect, versus an >exponentially increasing time penality. It may be that the root position is >just bad and looks worse with each additional ply. > >I was just curious as to whether this concept was worth considering, even for >"trivial" cases... but how likely are they to occur... maybe not worth the >hassle... > >Gordon Something is doable here. Deep Blue had some sort of algorithm that would extend the time when the tree was "unstable". And they didn't just define unstable as "fail lows or excessive move-changing at the root." They had something that Hsu briefly explained to me once several years ago, but there was a lot going on and I didn't pay close enough attention to remember enough to try it. They could recognize (at least for their program) when something unusual was going on and use more time to try to "search through" the problem and see what was _really_ going to happen... One day, I will think about it and ask them for an explanation again. This time I'll take notes. :)
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