47

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 ...


36

The answer by MikroDel gives the commonly-used "Reinfeld values" of pawn=1, bishop=knight=3, rook=5, and queen=9 (kings are essentially worth an infinite number of points, because the game ends if it is lost). While this is a good guide, chess is rarely that simple. Many books will give the value of bishops as 3.5 instead of 3, simply because they are often ...


34

Why do chess engines fail to spot good moves in some positions? The reason are called forward pruning techniques (see http://chessprogramming.wikispaces.com/Pruning) with ProbCut in first line. The move 15...Bf2 is pruned on shallow deeps because it includes the sacrifice 16.Rxf1 without regaining something concrete with evidence immediately after. The ...


27

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+)


21

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 ...


19

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 ...


17

Pawn - 1 point Bishop, Knight - 3 Pawns Rook - 5 Pawns Queen - 9 Pawns The evaluation depends on the position. In some situation you will find it equal or good to give you Rook and Pawn (6 Pawns) for Bishop and Knight (6 Pawns). But it is also possible that two light pieces are more valuable than Rook + Pawn. The value of pieces given to you will be a ...


17

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


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

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 ...


14

Different engines have different "scales" for their numerical evaluations. For instance, in a typical middlegame position with plenty of play left, when Houdini says +2.00 or better, it is highly probable that White has a winning advantage (though even here I've included qualifications for a reason). But consider: one could modify the source code of Houdini ...


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 ...


13

There's a great analysis/article about this by GM Larry Kaufman available here. To summarize: Pawn = 1 Knight = Bishop = 3.25 Bishop Pair = 0.5 Rook = 5 Queen = 9.75 There's also a lot more detail in the article about what situations favor which groups of pieces. For example, when B+N is better than R+P, or when Q+P is better than R+R, etc.


13

I am trying this with Houdini 1.5 (the free version). At first 15...Bf2 doesn't show up in the top 5 moves, then when it reaches depth 15, it does, as #1. Takes about 19 seconds on my four year old computer, not that long. So it doesn't fail to spot it, instead it only considers it the best move once depth 15 is reached. Apparently, as long as it only looks ...


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.


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 ...


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 ...


9

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


9

Black is down material but still has some strength. The most obvious one is that he has a pawn majority on the queenside, meaning potentially passed pawn if he manages to push his majority. So Black's plan will be to put both rooks behind the pawns and go for ...a5-a4, ...b5-b4 etc... In a very simple way White can fight against Black play (it's prophylaxie)...


9

As pointed out by Glorfindel, these are evaluations, which tell you who the engine thinks is better. A positive score means white is better, a negative black is better and values around zero mean that both sides are equal. These evaluation values are (traditionally) displayed with two decimals which is much too high precision for humans. In practical play ...


9

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 ...


9

It would be easy to detect sacrifices- if the material count in the position suddenly drops, but the computer evaluation position doesn't drop a lot, and the material isn't restored within a short number of moves (to avoid simple exchanges being considered sacrifices), then it would be a sound sacrifice. This would miss out on a lot of unsound sacrifices or ...


8

Though one cannot trade one's king for other considerations -- and in this sense the king cannot be evaluated -- the king still has a practical strength as an attacking and defending piece in the many concrete positions in which no immediate mate is in view -- especially during the endgame. This strength can indeed be evaluated. World Champion Emanuel ...


8

There are a couple of things here. First, each program is going to have its own way of evaluating positions so the scores can't be directly compared. For example, I was running StockFish against Rybka recently and found Stockfish's scores were about double those of Rybka. I was surprised by this, but it's pretty clear that a score of 1 doesn't always mean ...


8

A gambit can be proven to be unsound by using a modern chess engine. Having said this, I would like to mention a comic gambit, known as the Fred defense: [FEN ""] 1.e4 f5 2.exf5 Kf7 3.Qh5+ g6 4.fxg6+ Kg7 5.gxh7 Rxh7 6.Qg4+ Kh8 White has picked up 2 pawns. In return, the black king has done an artificial castle and black's pieces are ready to develop and ...


8

Sorry, computer engines are not designed to think like a human. It's a machine, it's written to play strong chess. There is no intelligence in there to think like that. The "good moves" you mentioned were actually bad moves at Stockfish's level.


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