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Comment by nerdy | Hacker News Reader

I'm very interested in the values assigned to pieces. Does anyone know the source or reasoning behind the table in step 2?

How are pieces relative values calculated? What's to say a pawn is 1/3 of a rook or a knight?

And why is the king 900, not simply the total value of all other pieces or slightly more? 8 pawns (10 ea), 2 knights (30 ea), 2 rooks (30 ea) and a queen (90) totals 290 points. Why can't a king simply be 300 points? If it needed to be worth more than both sets (white and black) for some reason why couldn't it be worth 600? The value 900 seems arbitrary to me.

If there's sound reasoning behind this can anyone recommend material related to deriving similar weighted values?

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Check out this chess programming wiki article [1] for a (still fairly hand-wavy) rationale for similar piece values, and the Wikipedia article on chess piece relative values [2] for a more in-depth look at various weightings. Some modern approaches use analysis of a huge corpus of master games to come up with piece values, but many of the systems are based on intuition and empirical evidence.

[1] https://chessprogramming.wikispaces.com/Simplified+evaluatio... [2] https://en.wikipedia.org/wiki/Chess_piece_relative_value

Good parent question and interesting links, thanks, will take a look.

To follow on though, shoukdn't it technically be the case that piece values should in theory fluctuate based on current situation.

For instance, my castle is worth zero to me if I'm throwing it so I can get you in check.

Will I know modern chess engines take this stuff into account. Mostly just a random thought.

> To follow on though, shoukdn't it technically be the case that piece values should in theory fluctuate based on current situation.

Yes. One common example is knights and bishops. Both are worth about 3 pawns, but knights are generally more useful in closed positions due to their ability to jump over pieces, while bishops are better in open positions since they can more attack and move long distances.

Fascinating.

So in some sense, and I'm just brain-farting here, the value of a piece is a weighted sum of all the possible squares it could occupy during move generation. Something like a rudimentary path trace.

Now trying my best not to get distracted building chess machines. :/

> values should in theory fluctuate based on current situation

The author touched this a little bit with adding the position adjustments

> my castle is worth zero to me if I'm throwing it so I can get you in check.

I know what you mean, but castling into or through check isn't a legal move and shouldn't show up in your list of possible moves.

Right, although I didn't mean castling into check. I meant tempting a greedy algorithm by throwing away a high value piece (which was always a weakness of early chess machines), although I realize the tree search would spot that.

Also now that I'm awake, read the article fully now.

Very cool, makes me want to try building one!

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