[Computer-go] pachi2

[valkyria at phmp.se]

Quoting Go Fast <fastgo at gmail.com>:

> I do not see any difficult in handling the second example.
>
> Whenever the white tries to take out one liberty of the corner X group, the
> 2-lib check should kick in and immediately put the bottom O group into
> atarai and it has no escape at all.


Look. If white takes one liberty away from X that group has 4  
liberties. I do not undestand what you mean with a two liberty rule.  
But I fear you give it magic properties it does not have and it sound  
you made a tactical oversight from what you wrote.

The atari is a self atari  (X must connect the two X stones to the 5  
Xes) which means the two liberty white group has three liberties  
effectively. And since X needs to play an approach move and fill in a  
liberty X has effectively less liberties. This is a lot of  
computations to do and if you do it everytime any group loses a  
liberty you have a huge impact on the speed of the playouts.

Capturing 2-liberty groups everytime a 5-liberty neighbor loses a  
liberty is also not a solution to the problem it will just make a lot  
of unneccessary moves and bias the playout in new weird ways, because  
most such situation are not a semeai with an eye and approach move.

If this was trivial Petr and I would not independently struggle with  
the same problem.

Magnus

>
> On Thu, Jan 13, 2011 at 8:46 AM, <valkyria at phmp.se> wrote:
>
>> Quoting Petr Baudis <pasky at ucw.cz>:
>>
>>
>>>     O O . . . .
>>>     O O X X X X
>>>     . X O O X .
>>>     . X O . O X
>>>     . X O O . X
>>>
>>
>> Funny! This is exactly the kind of shape that I had to struggle with in
>> Valkyria and which I cover in my other reply.
>>
>> Magnus