Re: Using partial plys

[David Mechner <mechner@xxxxxxxxxxx>]

Jeremy Thorpe wrote:
> there is a simple mistake here. [...]
> if the value of the next moves are distributed
> fairly nicely (no huge gaps), the value of sente 
> should be about half the biggest move [...]

But there /are/ often gaps in the distribution -- for example a lot of
maneuvering goes on to get the "last big move" of the opening, middle
game, endgame. I guess it's an empirical question which approximation
would work better in practice.

Anyway, I'm agnostic on the issue - my main point was that all this
presupposes two things: a good static evaluation function to add the
sente adjustment to, and for finding the move values, and a way of
determining when positions are independent. If you have that, it seems
to me, you're so far ahead of the game that the precise rule of thumb
you use to guess at the value of sente probably doesn't matter too
much.. 

> on this topic, i would like to try probabilistic approaches to this
> question.  of course, we can prove that such a question has a
> deterministic answer, but since nobody can find this answer, it may
> have real meaning to compute this probability.  even if it dosen't,
> it would be more useful to have a module that gives output like '75%
> chance alive' than one that says 'alive' but is wrong 25% of the
> time.

I agree, this is a smart thing to do (that's what we do :). But I think
this is what most traditional programs do, in effect, with their group
strength. Group strength may not always take on values from 0..1 or be
explicitly interpreted as probability of surviving, but the effect is
probably similar: the weaker and the bigger the group the bigger the
evaluation penalty.

Unfortunately knowing that a group is alive with probability .75 is not
very useful for deciding how to play in a particular instance. What you
really need to play above the double-digit kyu level is a module that:
1) says 'alive,' 'dead,' or 'undecided' 
2) is right 90% of the time when it's confident,
3) tells you when it's not confident, and
4) is confident in a large proportion of positions of normal 
   complexity.

This isn't impossible, it's just hard.
Life and death is the critical subproblem of computer go.


> or--another thought: let's say you know that your stones can 
> be killed if you don't play, but you think that 75% of 
> programs out there can't find the right move.  
  [...]
> what do you think?

I think that's as self-destructive a way to think for a go program as it
is for a human player -- your mileage may vary.

-David

-- 
David A. Mechner            Center for Neural Science
mechner@xxxxxxxxxxxxxxxxx         4 Washington Place, New York, NY 10003
212.998.3580                http://cns.nyu.edu/~mechner/