darius comments on The Curve of Capability - Less Wrong

18 Post author: rwallace 04 November 2010 08:22PM

You are viewing a comment permalink. View the original post to see all comments and the full post content.

Comments (264)

You are viewing a single comment's thread. Show more comments above.

Comment author: soreff 06 November 2010 06:50:23PM *  2 points [-]

I'm confused or about to display my ignorance. When you write:

There are many fairly natural problems which are not in P. For example, given a specific Go position does white or black have a win? This is in EXP

Are you saying that evaluating a Go position has exponential (time?) cost even on a nondeterministic machine? I thought that any given string of moves to the end of the game could be evaluated in polynomial (N^2?) time. I thought that the full set of possible strings of moves could be evaluated (naively) in exponential time on a deterministic machine and polynomial time on a nondeterministic machine - so I thought Go position evaluation would be in NP. I think you are saying that it is more costly than that. Are you saying that, and what am I getting wrong?

Comment author: darius 07 November 2010 01:39:01AM 6 points [-]

"Does this position win?" has a structure like "Is there a move such that, for each possible reply there is a move such that, for each possible reply... you win." -- where existential and universal quantifiers alternate in the nesting. In a SAT problem on the other hand you just have a nest of existentials. I don't know about Go specifically, but that's my understanding of the usual core difference between games and SAT.

Comment author: soreff 07 November 2010 03:21:11AM 0 points [-]

Much appreciated! So the NP solution to SAT is basically an OR over all of the possible assignments of the variables, where here (or for alternating move games in general), we've got alternating ORs and ANDs on sequential moves.