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Threats and Capturing

The second group of advisors deals with capturing interactions (in general, threats and conditions enabling threats):

local-threat:for each target piece which a piece could capture in the current position, this measures the value of executing this threat (based on the other advisors), but reduces this value based on which player is to move. Thus a threat in a position where a player is to move is almost as valuable for that player as the value derived from executing it (i.e. he can capture if he likes), but if it is the opponent's move the threat is less valuable, as it is less likely to happen. Thus attacking an enemy piece while leaving one's own piece attacked (if the pieces are of equal value) is a losing proposition, but if the threatened enemy piece is worth much more this may be a good idea. The value of these threats are also augmented based on the effect of the capture.

potent-threat:this extracts from the local-threat analysis just those threats which are obviously potent. A threat is potent for the player on move if the target is either undefended or more valuable (based on the other advisors) than the threatening piece. A threat is potent for the non-moving player only if the attacker is less valuable than the target and the moving-player does not already have a potent threat against the attacker.

global-threat:The two threat advisors above exist in both local and global versions. The local version credits a player for each threat she has in a position, while the global version credits the player with only the maximum of those local threat values.

possess:In a position where a player has a piece in-hand, the player is awarded the dynamic value (using the local advisors) that the piece would receive, averaged over all empty board squares. Note that if the maximum value were used instead of the average, a program searching one-ply would never choose to place a piece on the board once possessed.