[computer-go] On expanding the UCT tree

[Chris Fant]

> Like most of the UCT programs (I believe), Orego adds one tree node per
> Monte Carlo run. At present, this node includes data from the run that
> created it. Thus, after the first run, my tree looks like this:
>
> ROOT: 1/1 wins
>  CHILD A: 1/1 wins
>
> Ignoring the other children, I eventually do another run through that child,
> getting this:
>
> ROOT: 1/2 wins
>  CHILD A: 1/2 wins
>  GRANDCHILD B: 0/1 wins
>
> My concern here is that that there have been two runs recorded in node A and
> only one in node B. Does this cause a problem for the UCT formula, which
> assumes that the number of runs through a node is the sum of the number of
> runs through the children?
>
>

I think the effect would only be a problem if you are using the
memory-saving technique of not expanding a leaf until you have been
through it many times (100, for example).

I'm running a test of this now.  Regular UCT vs UCT with a
modification: subtracting 100 from the parent node visit count in the
UCT formula (actually 99 to avoid taking the log of zero).  Both
agents suppress node expansion until the leaf reaches 100 visits.