[Bug-gnubg] Neural network symmetry question

[Frank Berger]

Hi Mark,

> If I take a given board and translate the position into the inputs and then 
> evaluate the network, it gives me a probability of win. If I then flip the 
> board's perspective (ie white vs black) and do the same, I get another 
> probability of win. Those two probabilities should sum to 1, since one or the 
> other player must win (or equivalently, the probability of white winning = 
> probability of black losing = 1 - probability of black winning).


I assume your assumption is wrong. IIRC in an earlier paper there was an input 
to indicate who's on. It is much simpler to present the position from the point 
of the moving player, because the net has to learn less. I'm not that familiar 
with the gnubg code, but I think they do it in this way, so you can't just turn 
the perspective.

ciao
Frank