Re: [Bug-gnubg] crashed position

[Mark Higgins]

Revisiting this one - I read the eval.c ClassifyPosition code, so have a decent idea of how gnubg defines "crashed" (it's not what I described below).

What I don't get is why it uses this particular definition.

ie I'd imagine a crashed position is one where you're bearing in against an opponent anchor and have to start dismantling your beautiful barricade as the checkers come in.

So why isn't crashed something simple like "contact, and at least one player has all their checkers at their nine point or closer"? Seems like that's roughly when you'd start caring about how to bear off against an anchor. 

Or maybe you'd replace "nine point" with "six point" if you want to get closer to the end of the game. But I don't really see why how many checkers are on the 1 or 2 point specifically matter than much (vs the 3 point, or why >1 checker is the threshold vs >0 checkers).

Anyone remember the motivation for the current definition? 

On Dec 17, 2011, at 12:22 PM, Øystein Schønning-Johansen wrote:

On Sat, Dec 17, 2011 at 4:05 PM, Mark Higgins <address@hidden> wrote:

I'm trying to find the exact definition gnubg uses for a "crashed" position.

The one reference I've found (Thomas Haug's thesis) says it's contact, plus the restrictions that the player has fewer than 7 pieces remaining with none in the opponent's 1 or 2 position. Is that correct? 

If so, can someone give a little color on why those particular restrictions? eg why is it contact if the player has a piece on the opponent's 2 position, but crashed if it's on their 3 position?

The source is the documentation!

http://cvs.savannah.gnu.org/viewvc/gnubg/gnubg/eval.c?revision=HEAD&view=markup

Search for the function called ClassifyPositon()

-Øystein