Newbie question about capabilities

Newbie question about capabilities

Postby Wulff » Mon Sep 22, 2014 9:05 pm

Hi,

I just tried FinalGen 1.4 for the first time ever, using a "simple" position that I know the solution for (At least I think I do) :D

The position is this one: 4K3/6pk/7p/6P1/8/8/P7/8 w - - 0 1

I believe this should be a win for white in 8 moves, starting with 1. g6+ but finalgen says no.
Someone with the kppkpp tablebase should be able to verify this.

Shouldnt finalgen be able to solve this one correctly, or does it not handles pawns only positions ?

Any help would appreciated.
Wulff
 
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Re: Newbie question about capabilities

Postby duncan » Tue Sep 23, 2014 8:11 pm

do not know much about chess, but http://www.k4it.de/index.php?lang=en&topic=egtb says it is a win for white in 19. final gen says g6 is unsolved. possibly because black has an option to queen together with white


viewtopic.php?f=3&t=37

When a pawns promotes, the generation continues in "bitbase" mode. Then 2 things can happen:
1- It finds a way to checkmate without a second promotion on the same side => then the result is "win".
2- A second promotion on the same side is necessary to prove a result => the second promotion is not examined and the result is "unsolved".

If both sides can force a promotion, then Finalgen can handle some situations in which one promoted piece gets captured after one or more moves, otherwise the result will be "unsolved".

In the case of pawn endgames, after promotions we can transpose to a position with 1 piece per side. Even if those positions can be theoretically handled, in practice they are not.
So, only one promotion is supported.
duncan
 
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Re: Newbie question about capabilities

Postby pPerez » Wed Oct 01, 2014 9:08 am

Wulff wrote:I believe this should be a win for white in 8 moves, starting with 1. g6+ but finalgen says no.


Hello,

FinalGen did not say "no", It just said "I don't know".
One of the limitations of FinalGen is that it is not able to solve all positions. Some of them can remain unsolved.
But when FinalGen gives a definite result ("win", "draw" "lose"), it is 100% guaranteed, because positions are analysed until the final mate, stalemate or infinite repetitions.

All of these things are explained in the tutorial.

In this particular position, as Duncan explained very well, the pawn ending needs to transpose into a queen ending to be solved, and this is a situation that FinalGen cannot manage.

Regards,
Pedro
pPerez
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Re: Newbie question about capabilities

Postby Vetinari (engine) » Fri Oct 03, 2014 9:06 pm

But I have to agree to Wulff, it is strange. Yes, black is able to promote his pawn. But in the same move the new Q is captured. Doesn't finalgen try a few moves if there is a quick win?
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Re: Newbie question about capabilities

Postby Wulff » Sat Oct 04, 2014 1:14 pm

Vetinari (engine) wrote:But I have to agree to Wulff, it is strange. Yes, black is able to promote his pawn. But in the same move the new Q is captured. Doesn't finalgen try a few moves if there is a quick win?

Just to clearify, the queen is NOT captured, as that would result in a stale-mate.
Wulff
 
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Re: Newbie question about capabilities

Postby Vetinari (engine) » Thu Oct 16, 2014 12:15 pm

Oh; sorry, I didnt take into consideration that black isn't forced to take that pawn. This explains it: finalgen tries out a few moves after promotion and doesn't find immediate win because the mate is behind its "horizon".
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Re: Newbie question about capabilities

Postby pPerez » Tue Oct 21, 2014 1:16 pm

Yes, in that particular position, the queen cannot be captured after the promotion, so it actually transposes into a queen ending.
So, the position is unsolved because two promotions are required to solve it.
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