[Computer-go] pachi2

[valkyria at phmp.se]

Quoting Petr Baudis <pasky at ucw.cz>:

> On Thu, Jan 13, 2011 at 10:25:28AM -0500, fastgo wrote:
>> I guess we are not talking about the same case or I may have misread the
>> issue or the example. I was commenting on the second example. My take is
>> that it is corner as Petr stated "Example is the other bottom corner of the
>> same game:"
>>
>>     O O . . . .
>>     O O X X X X
>>     . X O O X . 3
>>     . X O . O X 2
>>     . X O O . X 1
>           P R S T
>
>>
>> I meant to say that if it is corner as the diagram shown, then the playout
>> should almost always get it right. As the middle bottom white group has only
>> 2 liberties left and the left black group has 3 liberties. Any attempt by
>> the white group to take one liberty of the left black group will trigger
>> black to immediately check its surroundings and kill the white group.
>>
>> Even in cases where the liberties of the 5 liberty group are played first by
>> the white group, and when it goes down to 2 liberties, the black will check
>> its surroundings and kill the bottom white group first.
>
> No, if white takes any liberty of the left group, it is over - black
> loses the semeai. The white group has effectively three liberties - R2,
> S1 and T3.

Ok. But the diagram does not display enough context. If it is in the  
bottom right then the 3 Xs could be safely connected. But is also true  
that 5Xs could also be safely connected. So I just see what I had in  
mind when I wrote my first longer posting.

This confusion is exactly what happens in montecarlo playouts because  
analyzing the complete context is too timeconsuming. Understanding the  
nature of this semeai depends on more than the liberties in the  
diagram. In Valkyria I therefore also have to check if these liberties  
are "semeailike" or open as in the sense the Xs can easily get more  
liberties. Otherwise the accuracy would get way to low. Still this is  
only approximate so it still makes a lot of mistakes, which need to be  
covered by tree search.

Best
Magnus