Re: Advice on evaluation

[Joan Pons Semelis <joan@xxxxxxxxxxxxxxxx>]

I did not express myself clearly. My answer to your 
question about 2 values "what if is B/W turn" was yes,
the post was a reasoning of why. 
I've also found Mark Boon problems about playing
sente moves to keep the 2 unsettled groups from
dying, it's a common problem with lookahead with
inperfect evaluating functions that chess people
call "horizont effect": the program pushes the problem
beyond the horizont so that it disapears. But making
simptons disapear doesn't cure the disease, pragmatical
as it may be.
My example of ladders might seem to imply "hard" lookahead
to decide about groups status, it's not necessarily so, I
completely agree with you in that it can't be used for group
strength, at least in general, but I did'nt said so:

>From my previous post:
>  >With group strength the evaluation to decide if it's instable
>  >it's more complicated than "1 or 2 liberties", the moves to

What I meant is that I want to know for a group the answers to the
questions " Can it be killed?" and "Are there sente moves against it ?"
as well as I do with 2 liberties chains of stones. In this later
case I can find the answer reading all the necessary moves, in the former
I need to estimate a plausible answer, as actually reading out the problem
is not practical and in most cases unnecessary, but the idea is the
same, only in one case the function that answers yes/no is accurate
while in the other is estimating. How do you use this information for
deciding on a move is another story, and here is when the "horizont
effect" takes place if just minimax is used to decide for a move.
A goal oriented approach seems better.

I hope my point of view is clearer now.

Joan

PS: That function that guesses sente moves against weak groups?
    Did you heard about the holy grail ? :-)

From: David Fotland <fotland@xxxxxxxxxxxxxxxxx>

>   No, most group strength evaluations can't be decided by
>  reading.  Take a look at a typical early middle game position
>  from your own games.  There are lots of stable groups that
>  don't have two eyes yet.  But if the opponent is a little
>  thicker, then you want to add a stone.  Evaluating this
>  relative thickness is very difficult.
>    
>  When there is a fight that can be decided by some tesuji, of 
>  course you can try to read the result.  But you want the
>  group strength evaluator to first tell you that here is
>  a fight.  You don't want to waste time reading when your
>  stones are already dead.
>  
>  David