Value of a group

[Darren Cook <darren@xxxxxxxxxxxxxx>]

Is a group worth saving? If there are two groups on the board, and I can
only save one, which one should I save?

Or when doing life/death reading, which groups should we concentrate on, and
which groups are not important?

To answer these questions we need to know the value of a group. I'll suggest
some simple algorithms below, and perhaps people on this mailing list can
suggest further improvements and ideas.


SIMPLE ALGORITHM
Number of stones x 2.

A group with 10 stones is worth 0 points if it lives, 20 points to enemy if
it's captured (Japanese scoring).


BETTER ALGORITHM
Number of stones x 2, plus territory of that group x 2.

Okay, that's not an algorithm. Territory could be defined as the sum of
points found by searching out (using a 'fill' algorithm) from liberties
until enemy stones are reached. Ie. if an enemy stone is adjacent to a point
it can't be territory (and we also don't search out any further from that
point).

A group of 10 stones with 6 points of territory is worth 6 points if it
lives, 26 points if it's dead (assumes the enemy gets all that territory). A
difference of 32 points.


PROBLEMS
1.The enemy might have to fill in some of the territory to capture it. So
it's worth less.

2.If this group lives, it may mean that other enemy groups die. If it dies,
those enemy groups might live.

Eg. a 32 point group in semeai with a group worth 24 points --> a move that
kills the enemy or makes us live is worth 56 points?


Any comments?

Darren