Lyudmil Tsvetkov wrote:
I never understood those imbalances, they simply seem not to obey any reasonable adjustment rule.
The question of imbalances is complicated in SF. It has inherited this code from Glaurung, including a quadratic function which obfuscates the code and makes it difficult to tune the values. That's why no one wants to mess with it. Gull has a similar quadratic function for imbalances.
My idea (barring changing all this code) is to follow the values 'Material' and 'Imbalance' in the evaluation table for various postions and try to change those through tweaking of the multiple constants that affect material and imbalance.
Seeing the evaluation table for various positions is easy, and I can show it if you don't know already.
I have always been somewhat reluctant to tune piece values, because I have a lot of other material scoring terms (for particular kinds of imbalances, for example) that would interact with them. These would all have to be tuned together.
FYI SPSA is known to have slow convergence near the end of a tuning cycle. I have an implementation of an improved version (RSPSA) here: https://github.com/jdart1/arasan-chess/ ... /rspsa.cpp that does better in that respect.
But I have also been using this software: http://www.adrl.ethz.ch/doku.php/adrl:software (designed for a robotics application), which in my experience converges even faster. The author is working on adding support for box constraints.
Of course, Pawel made a great discovery that attacking enemy pieces on the long diagonal is essential for the trick to work, and we should all be grateful to him.
But besides from this, we should also try to somehow reflect the king safety aspect of the fianchettoed bishop.
Here is my vision:
- king fianchettoe will ne any bishop on g2,h1.f3
- add 5cps bonus for any enemy piece, rook, knight or maybe queen on that diagonal; add another 2cps for any enemy pawn on that diagonal, so here we somewhat develop the idea of Pawel, as attacking pawns is also important
- add another 2cps bonus for any own pawn on square adjacent to the bishop, either in front of the bishop or next to it; this will reflect the king safety aspect of the bishop, as pawns go forward, the safety bonus will be lowered
The very nice thing about this implementation is that it will automatically adjust the value of the bishop on the long diagonal in terms of available enemy objects to attack and own pawns providing king safety, so the engine can wisely decide if it makes sense to fianchettoe, or maybe it is better to develop the bishop in the center.
[d]r1bq1rk1/ppp1bppp/2n1pn2/3p4/2PP4/5NP1/PP2PPBP/RNBQ1RK1 b - - 0 1
above, you give 5cp to Bg2 for attacking black Nc6, anoter 5cps for attacking black Ra8, another 2cps for attacking pawn on b7, 2cps for pawn on d5, 2cps each for white pawns on adjacent f2,g3 and h2 squares.
Total bonus will be 20cps.
When Nc6 is not on the long diagonal, Bg2 will get 5cps less, when Ra8 gets to Rb8 another 5cps less, when the b7 pawn advances, another 2cps less, etc.; also, when white h2 pawn advances to h4, another 2cps less, when g3 pawn advances to g4, another 2cps less, etc.
So this automatically adjusts the value of the bishop, which is really very nice and might help you to tune the bonus of the bishop with other relevant psqt/mobility terms easier.
What do you think of this further refinement?
Anyone besides Pawel having tried to implement this?
Maybe someone of the SF team will also get interested, as SF badly needs this term.
Why is it important to score enemy pieces on the long diagonal?
well, a bishop on any other diagonal might attack one or 2 enemy objects at most at a time, while a bishop on the long diagonal might attack up to 5! enemy objects, on squares e4,d5,c6,b7 and a8; so this is a special case of x-ray attacking
Why is it important to score own pawns on adjacent squares?
well, very simple: a king with pawns around it is safe, a king with bishop around it is somewhat safe, and a king with pawns and a bishop around it is safest. So you clearly should reflect this special case of king safety.
Lyudmil Tsvetkov wrote:I think also the king location should be restricted to h1,g1,h2, as other king squares are more or less irrelevant.
Of course, the king fianchettoe can also happen extremely rarely on the queen side, when king is on b1,a1,a2, with Bb2.
Actually, the only player I have seen to frequently use this setup on the queen side is Fischer.
At the moment, SF doesn't know that fianchetto exists (no word 'fianchetto' in SF code). There were candidate fianchetto patches in the past which didn't pass, unfortunately.
Maybe a small bonus should be given to the f1/f8 bishop in the opening to sometimes go to g2/g7.
These values are too initial for any change in them to be successful. All the subsequent more particular values are tuned to those so some local optimum exists. It is hard steer away from it.
lantonov wrote:These values are too initial for any change in them to be successful. All the subsequent more particular values are tuned to those so some local optimum exists. It is hard steer away from it.
That is not the problem - the problem is that this simply does not work.
Joerg's initial values included the very non-sensical bigger knight value for the eg. Utterly lacks any sense. And yet it scores well.
Now, Joerg pushes a second patch with much more sensical lower knight eg value, and it quickly fails. It absolutely makes no sense. Absolutely.
Only reasonable explanation is imbalances are interfering again, but I do not believe that either.
I watched so many games where values should go exactly the way of Joerg's second patch and the patch that is currently running and going to fail in the same way, so many games, but the most reasonable thing fails. I absolutely have no explanation.
Well, maybe everything can happen at 15 sec. games, so the engine simply gets it all quite wrong, but I do not believe that either. It simply makes no sense.
lantonov wrote:These values are too initial for any change in them to be successful. All the subsequent more particular values are tuned to those so some local optimum exists. It is hard steer away from it.
That is not the problem - the problem is that this simply does not work.
Joerg's initial values included the very non-sensical bigger knight value for the eg. Utterly lacks any sense. And yet it scores well.
Now, Joerg pushes a second patch with much more sensical lower knight eg value, and it quickly fails. It absolutely makes no sense. Absolutely.
Only reasonable explanation is imbalances are interfering again, but I do not believe that either.
I watched so many games where values should go exactly the way of Joerg's second patch and the patch that is currently running and going to fail in the same way, so many games, but the most reasonable thing fails. I absolutely have no explanation.
Well, maybe everything can happen at 15 sec. games, so the engine simply gets it all quite wrong, but I do not believe that either. It simply makes no sense.
This is exactly what I tried to explain (to myself too) with the above. The values that are reasonable to you, are "unreasonable" to the program because all the other values are tuned to the values that are unreasonable to you.
