[Computer-go] useless ko threats

[ds]

Am Dienstag, den 06.03.2012, 15:35 +0000 schrieb 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.

The problem is even worse: if the playout does not handle using ko
threads, X would (most of the time) not have any disadvantage at all...

> 
> -M-
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