How did these errors manifest themselves in practise? It appears paradoxical to speak of a computer making calculating errors.
pawn = 100? 128? 256? 1000? Etc. The advantage of larger pawn values is that you have more room for ever-smaller positional bonuses. But when you think about it, is there any chance that a difference of 1/1000th (or 1/32000th) of a pawn is going to lead to a revolutionary evaluation? I'm hardly the best evaluation person on the planet, no idea who would actually hold that title. But I have done both 100 and 1000, and found absolutely zero difference in terms of playing skill. It simplifies thinking, as you now only agonize over units of 1/100th for a bonus, rather than having 10 times more possibilities, most of which are completely random in the third digit anyway. The debates range from one end to the other. A larger score range makes the evaluation more accurate. It makes the search less efficient. Smaller scores make the evaluation less accurate but the search more accurate. My take is that I am not qualified, and I have never found anyone that was, to be able to use even 1/100ths of a pawn units, much less 1/1000th or smaller. One of the more famous evaluation books written many years ago (not for computer chess) was "Point Count Chess" and the author generally worked with 1/10th of a pawn units.
There are also hybrid approaches. Use really large scoring ranges and then scale back before using the score at the end of the evaluation. No particular point, pro or con, to doing so.
>The advantage of larger pawn values is that you have more room for ever-smaller positional bonuses<
I must be missing something here. Larry Kaufman said pawn values were in his opinion too low for Rybka 1, which led to R1 being oblivious to dangerous, connected passed pawns, especially during material imbalances. He thus raised the pawn value in Rybka 2.32a.
How is this compatible with a base value of 3200 in Rybka 1.0 Beta?
>I must be missing something here.
He means more precise values, not the values themselves.
You would use integers like 10,100,1000 instead of 0.5, 1.2 etc. to simplify the math, and there might be some performance benefits as well (not sure). So you'd make all the piece values the same order of magnitude and make adjustments therein (ie. 1/3/3/5/9, 10,30/30/50/90, 100/300/300/500/900, and so on).
The other issue, that Bob was talking about, is whether it is better to assign higher values to all pieces (such as 3200 for a pawn), in order to allow more fine-grained distinctions.
We have jokingly called these scoring values pawns, centipawns (pawn = 100), millipawns (pawn = 1000). You could take this all the way to micro pawns (pawn = 1000000). My question is, can you REALLY get so precise that you can say here, this positional score is worth 112, while in this position it is worth 114? As a human, even centipawns is probably a stretch for most things. And millipawn units are probably too small to be useful. Now if you use auto-tuning, where humans are not involved, then one might make a case for micro pawn units, or nano pawn units, or pico or femto, etc. But when you display the scores, a human could not interpret them very well.
For example, what if your ruler has micro-inch markings on it (1/1000000th of an inch)??? not useful to me at all. Even in hot rodding, 1/10000th is highly accurate.
>For example, what if your ruler has micro-inch markings on it (1/1000000th of an inch)??? not useful to me at all. Even in hot rodding, 1/10000th is highly accurate.
I've actually always wanted a meter long ruler, with markings for cm, mm, μm, and nm. Even though I wouldn't be able to see the nm ones without an electron microscope, would be cool to know they are there :-P
The main difference here is that the White pawns code in Rybka 2.3.2a proceeds
to count how many such pawns have no mobility, subtracting (42, 339) for each.
One of the things that I felt was wrong with Rybka (all versions thru 2.3.1) was that
she undervalued pawns relative to pieces, so that she would almost always play to win a piece
for three pawns, sometimes even for four, even when the pawns were rather dangerous (others
have said so too). Correcting this without bad side effects was not trivial, but eventually I
found the values that corrected the problem while showing an improvement in overall strength
of a couple points at the same time. [...] Roughly speaking, Rybka 2.3.1 and earlier versions
consider that a piece (knight or unpaired bishop) is worth about four pawns in the middlegame,
even more on a full board. I think this is going too far. I would say that a fair value for a
knight or unpaired bishop is about 3 1/2 pawns in the middlegame, somewhat higher in the
opening, and version 2.3.2 is fairly close to my view on this.” Kaufmann
End of quote.
However, other parameters in 2.32a were suboptimaly tuned compared to version 1 to 2.2.
Rybka 2.32a got inflated queen values :http://tartajubow.blogspot.se/2011/03/engine-positional-evaluations-and.html
Rybka 1.2 conciders the position with a queen and pawn for 3 minor pieces advantageous for white( CORRECTLY). 2.32a conciders the position drawn, with a slight lean towards black.
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