[Computer-go] pachi2

[valkyria at phmp.se]

I know the source of the confusion now. The first example was "Bottom  
left corner of 19x19 board" as Petr wrote it so the corner in the  
second example must be the bottom right. If it is located in the lower  
left corner then all you wrote made sense, but I am talking about the  
case where there is a "1-approach liberty" whcih is only for the case  
where this pattern is located in the lower right corner and is much  
hardwer to solve correctly.

:)

Magnus

Quoting fastgo <fastgo at gmail.com>:

> 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 .
>     . X O . O X
>     . X O O . X
>
> 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.
>
>
>
> On Thu, Jan 13, 2011 at 9:42 AM, <valkyria at phmp.se> wrote:
>
>> 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
>>>>
>>>
>>
>>
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>