[Computer-go] useless ko threats

[Matthew Woodcraft]

Stefan Kaitschick wrote:
> Bots love to throw in useless ko threat type moves now and then.
> Sometimes its just a wasted threat, at other times it loses a useful
> liberty too. Why do even strong bots show this "stupid" behaviour?

> Ko threat type moves have one thing in common: a big payoff if the
> opponent answers incorrectly. If the first response tested is wrong,
> then the ko threat will start off with a very good winrate. The
> correct response will be found fairly soon, but by then the original
> move will have a winrate bonus.

> This bonus is small, but it is there. The problem is, that the winrate
> degradation, that a useless ko threat causes, can also be small. So if
> the (erroneous) bonus outweighs the (real) loss, the bot will conclude
> that throwing in the ko threat is good.


I think it's a little more complicated than that.

Suppose that X and Y are a ko threat and its only response, and A is the
'best' move (the move that the computer would play if the ko threat
wasn't an option).

Then X is competing against A.

X has a (large) advantage for each time the 'opponent' fails to choose
Y, but it also has a disadvantage for each time the 'player' chooses a
move other than A in the position after X-Y.

-M-