[Computer-go] useless ko threats

[Don Dailey]

On Tue, Mar 6, 2012 at 5:00 AM, Stefan Kaitschick <
stefan.kaitschick at hamburg.de> 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?
>
> Lazarus had that problem too and before that my simple bot had it really
badly because it did not have the benefit of a tree search.     I don't
know if discounting the move is a reasonable solution or not, perhaps it
is.   But I think that if you can solve it in the playouts you solve it in
general.     You almost need to determine in the playout how to refute a
stupid ko threat but I don't think that is simple at all.

Don




> 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.
> To remedy this, I think the winrates of early replies that prove
> ineffective, have to be discounted from the parent node.
> I know its not as easy as it sounds, because the winrate also directs the
> search.
> I'm not proposing a method here, just pointing to the problem.
>
> Stefan
>
>
>
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