48
I am not an expert on stockfish source code, but my understanding is the following.
Humans:
It is true, that the 1 piece equals 3 pawns approach is pretty accurate, surprisingly so. However as you are probably aware, when evaluating a position, we consider many other aspects as well, such as piece activity, space, king safety, etc. The difference however ...
37
I'm pretty sure Stockfish doesn't have explicit code that handles opposite-side castling. What it does have is:
Some kind of "menace" score for enemy pawns advancing against our king. The closer they get, the more dangerous Stockfish thinks they are.
Some kind of "pawn shield" score for friendly pawns in front of our king. The fewer ...
28
This is a fortress and a draw.
The black king can't advance as the rook, shuffling between h3 and f3, prevents it. The only way to break the fortress is to trade the queen for the rook and pawn, but the resulting endgame is still a draw.
26
When I said chess is a zero sum game in that answer, I wasn't referring to anything involving ratings. Obviously if we include ratings then chess isn't strictly a zero sum game, since the gains and losses aren't always balanced out. But different rating systems are arbitrary, and aren't part of the game of chess itself.
Your question should be "Is the FIDE ...
23
It's because 1. exf8=Q+ Kxh7 2. Rxd7?? would be stalemate. I think it is a even a theoretical draw after 1. exf8=Q+ Kxh7 2. Qg7+. Therefore 1. exf8=B+! (with check!) is better, since white then can keep an extra piece and win easily.
[FEN "5r2/3qPbkB/8/7P/8/8/8/1K1R4 w - - 0 1"]
1. exf8=Q+ (1. exf8=B+!) Kxh7 2. Rxd7? (2. Qg7+)
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Individual pieces:
Pawn - 1 point
Knight - 3 points
Bishop - 3 points
Rook - 5 points
Queen - 9 points
Piece combinations:
Rook and Knight - 7.5 points
Rook and Bishop - 8 points
Pair of Rooks - 10 points
Three minor pieces - 10 points
Rook and two minor pieces - 11 points
N.B. The values may vary because of circumstances, but these are the basic values.
22
There is a very easy way to detect whether King and Pawn endgames are drawn or not.
This method I use is a very easy to understand one from Karsten Mueller and Frank Lamprecht's excellent book Secrets of Pawn Endings
It concerns key squares and opposition
The rule states that if pawn has not reached or crossed the central line (5th rank for White and 4th ...
22
This position is a standard classical fortress. There is no way the Black color can go through as long as White just shuffle pieces, wait and do nothing silly.
Stockfish is a computer algorithm, it has no intelligence. It doesn't know it's a draw unless it searches for all the possibilities, but it's practically impossible.
Connect to a 6-piece tablebase, ...
20
If the engine can choose between getting mated in 2 or mated in 3, it'll choose the line where it is mated in 3 (even though the mate in 2 might be 'more difficult' to spot for humans).
It can't really set traps, because it doesn't know what things might be difficult to spot for a human (or other engine) opponent. It just evaluates the position, without ...
20
Is there any established system for evaluating positions taking into account time for both players?
No, there isn't. This is for two main reasons:
There is no objective measure for how time affects a player's ability to play any given position.
Such evaluations would be useless. They would literally tell you nothing useful
Let me give an example from a ...
20
What I can't wrap my head around is that Stockfish says that this position is completely equal. Why is that?
Black has the bishop pair in a completely open position (no center pawns). This advantage plus the extra open b file, which black is ready to exploit with Rb8, compensates for the doubled isolated pawns.
19
It just seemed obvious to me that gambits would work better with faster games, for the same reasons as given in the comments - it's harder to defend than attack, etc. I tried looking at several gambits in the lichess database to support this theory.
In classical+rapid games, White wins 53% of Evans Gambit games vs 43% for Black. In bullet+blitz games, it's ...
18
The Site ratings at slow time controls can be quite reliable for servers where strong players congregate (ICC, FICS to name a few) as the ratings VERY closely reflect your true playing strength if you've played enough games. For very standardized rating systems such as USCF and FIDE/ELO, you will notice that the different rating classes tend to point to the ...
18
By playing 11...h6, you created a weakness on g6, and you created a target on h6, now it is easier for white to open up a position around your king by pushing their g-pawn. White also has a potential bishop sacrifice on h6.
In general it is best to avoid pawn moves in front of your king, especially when facing a pawn storm.
17
Those aren't scores; there are just three possible scores in chess: White wins, Black wins, and draw.
Those are evaluations of the chess engine; a score of +0.62 means the engine thinks White's position is better by 0.62 pawns. A negative score would mean Black is better. On professional level, a score of 1.5 pawns is in most positions decisive, i.e. enough ...
16
Interesting question. I think it depends on how much bottom-up intelligence the engine has. For example, AlphaZero was given no explicit heuristics, but was able to infer plenty of strategy by playing itself millions of times and learning that way.
An engine with explicit heuristics can also exhibit additional strategies you didn't program into it. As a non-...
14
The best way to normalise a centipawn score to [-1,+1] range is using a sigmoid function, as that closely approximates the likelihood of a given centipawn advantage converting to a win, and avoids the need to identify a strict maximum or minimum. This is discussed here.
14
Chess is a zero sum game. There is 1 point available and it is divided over the players, what one gains the other loses. It is a simple concept with a simple answer. Tournament rules mention some very rare cases where the result is 0-0 or 0.5 - 0, but in my opinion those are "outside the game". That a mobile phone may ring is not really a matter for the game ...
14
[FEN "r4rk1/2p1qppp/1p3n2/p7/2B4B/4P3/PPQN1Pbb/2KRR3 w - - 0 1"]
1. f3 {traps the bishop} Rad8 2. Re2 Bxf3 (2...Bd6 Rxg2 Kh8 Rh1 {the Black king is not safe at all}) 3. Bxf6 Qxf6 (3...gxf6 Rxh2 {checkmate on h7 will follow}) 4. Rxh2 {threatening mate on h7} h6
5. Rf1 {the bishop is now pinned against the queen and will be won shortly} b5 6. Be2
...
12
A good chess engine won't stop after a predetermined number of moves, but will keep looking until the position is "quiescent", which roughly speaking means that there are no pending captures or checks. See Quiescence Search in chessprogramming wikispaces for a more detailed explanation.
12
To add to the existing answers, you just gave up your light squared bishop for no apparent reason, while creating many light square weaknesses around your king with the same move! Now white is the only player with a light squared bishop and you will have a tough defensive job if white plays correctly.
11
White does indeed fork the king & rook after Nc7+ - but after Nxa8, the knight is not escaping, so Black is at worst even on material.
[FEN ""]
1. d4 c5 2. Nf3 cxd4 3. Nxd4 Nc6 4. Nc3 e5 5. Ndb5 Bb4 6. Bg5? Qxg5 7. Nc7+ Kd8 8. Nxa8
After something like ...b6 followed by Bb7, the knight's a goner. White can get at most one pawn for the knight (after ...
11
I agree with the other two answers, but I feel like I also need to comment on the beginning of the game since there was A LOT more important stuff there than just the answer to why Qxg5.
This is very similar to a Kalashnikov Sicilian by transposition with the exception that the knight is on c3 instead of a pawn on e4, but the ideas are very similar. In ...
11
Just because Stockfish thinks a move is best doesn't mean it is best. But let's see why Stockfish might like it.
When I look at Stockfish's static evaluation of that position, and move the king from c1 to b1, I see four sub-evaluations change. In order of the size of the change, those sub-evaluations are:
Psqt bonus. This gives a bonus to each piece based ...
11
Why is h4 much better than h3?
It's very simple. The prospects for the bishop are much better on g3 than h2. On h2 the bishop does nothing useful and it will take a lot of moves to get it back into the game via g1. Black will exert iron control over f4 with pawns on e5 and g5 making the freeing move f2-f4 impossible.
On g3 the bishop has a role protecting ...
10
I think this picture describes the situation quite well. It was created from 400k games, and considers only plain piece material.
Source: Pawn Advantage, Win Percentage, and ELO
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If I understand correctly your x axis is the moves. Your script implied Anand and Prag were blundering every time they make a move,
Clearly you have a bug in your script. Stockfish engine always give you a score relative to the player making the move, NOT white. You need to multiply the score by minus one if it’s Black to move.
Please do this and you will ...
10
First, I don't think that there is any doubt that black has significant compensation, but clearly, black is still trying to hold this, not win it when talking two computers playing each other. I believe that between two humans, I would probably prefer black.
If you have an eval that says +.63 for white, but black is down two pawns, you have to realize that ...
10
Please note that those values are "abstract", later to be modified by the specifics of the position. For example, even though a knight appears 0.8 pawns less valuable than a bishop, it could be that bigger bonuses are awarded to well-placed knights than for well-placed bishops, turning the balance around.
It's also worth noting that the "3 pawns equal a ...
10
Unless you explicitly hard-code these endgames, or provide the computer with endgame tablebases, they will apply what they've always done throughout the game: search lines and return the static eval (which is basically the evaluation function of the engine, evaluated on the final position). The static eval isn't smart enough to realize that this game is a ...
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