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16.1 Conceptual Outline of Influence

We define call stones lively if they cannot be tactically attacked, or if they have a tactical defense and belong to the player whose turn it is. Similarly, stones that cannot be strategically attacked (in the sense of the life-and-death analysis), or that have a strategical defense and belong to the player to move, are called alive while all other stones are called alive. If we want to use the influence function before deciding the strategical status, all lively stones count as alive.

Every alive stone on the board works as an influence source, with influence of its color radiating outwards in all directions. The strength of the influence declines exponentially with the distance from the source.

Influence can only flow unhindered if the board is empty, however. All lively stones (regardless of color) act as influence barriers, as do connections between enemy stones that can't be broken through. For example the one space jump counts as a barrier unless either of the stones can be captured. Notice that it doesn't matter much if the connection between the two stones can be broken, since in that case there would come influence from both directions anyway.

We define territory to be the intersections where one color has no influence at all and the other player does have. We can introduce moyo and area concepts similar to those provided by the Bouzy algorithms in terms of the influence values for the two colors. "Territory" refers to certain or probable territory while "Moyo" refers to an area of dominant influence which is not necessarily guaranteed territory. "Area" refers to the breathing space around a group in which it can manoever if it is attacked.

In order to avoid finding bogus territory, we add extra influence sources at places where an invasion can be launched, e.g. at 3-3 under a handicap stone, in the middle of wide edge extensions and in the center of large open spaces anywhere. Similarly we add extra influence sources where intrusions can be made into what otherwise looks as solid territory, e.g. monkey jumps.

Walls typically radiate an influence that is stronger than the sum of the influence from the stones building the wall. To accommodate for this phenomenon, we also add extra influence sources in empty space at certain distances away from walls.

All these extra influence sources, as well as connections, are controlled by a pattern database, which consists of the two files patterns/influence.db and patterns/barriers.db. The details are explained in 16.9 Patterns used by the Influence module.

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