Thanks Ian! That makes it a lot more clear.
On Feb 10, 2012, at 5:34 AM, Ian Shaw wrote: > I'll just emphasize Joseph's explanation. > > > Mark wrote: > " 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." > > This is not the essence of a crashed position. It's not about bearing in > against an anchor (although some of these will be in the crashed category). A > position is crashed if most of a players chequers have ended up on his own 1 > and 2 points, giving him little flexibility. He has no control of his inner > board or the outfield, which allows his opponent to spread his chequers > around without fear of being hit and contained. This calls for different > tactics from the standard contact positions. > > Perhaps a couple of diagrams will help (view with fixed-width font). Player X > has the same structure each time; the difference is in the opponent's > position. In the crashed position X can safely slot the front of the prime to > roll it forward, but this would be too dangerous when O still has good > structure. > > > GNU Backgammon Position ID: /z4AADBsuxsEAA > Match ID : cAngAAAAAAAE > +24-23-22-21-20-19------18-17-16-15-14-13-+ O: White > | O O | | X | 0 points > | O O | | | > | O O | | | > | O O | | | > | 8 O | | | > | |BAR| |v 7 point match (Cube: 1) > | | | | > | | | | > | X | | X | > | O X X X X | | X X | On roll > | O X X X X | | X X | 0 points > +-1--2--3--4--5--6-------7--8--9-10-11-12-+ X: Blue > > GNU Backgammon Position ID: sN0tADBsuxsEAA > Match ID : cAngAAAAAAAE > +24-23-22-21-20-19------18-17-16-15-14-13-+ O: White > | O O | | O O O O X | 0 points > | O O | | O O O | > | | | O O | > | | | | > | | | | > | |BAR| |v 7 point match (Cube: 1) > | | | | > | | | | > | X | | X | > | O X X X X | | X X | On roll > | O X X X X | | X X | 0 points > +-1--2--3--4--5--6-------7--8--9-10-11-12-+ X: Blue > > > I hope this helps. > > -- Ian > > > > > -----Original Message----- > From: [email protected] > [mailto:[email protected]] On Behalf Of > Joseph Heled > Sent: 08 February 2012 23:09 > To: Mark Higgins > Cc: [email protected]; Øystein Schønning-Johansen > Subject: Re: [Bug-gnubg] crashed position > > CRASHED attempts to capture the positions where one side has only a > small number of "active pieces". The number of active pieces has been > arbitrarily set at 6, and the definition requires that you have at > most 6 checkers not on points 1 or 2, accounting for the possibility > of one checker from 2 sent back after the rest piled on point 1. > > The most important part in this celebration of arbitrary decisions was > to use a definition which is non cyclic - positions resulting from a > crashed positions should be crashed. When this is violated, > performance deteriorates since each net is trained only on it's own > kind of positions. > > That was my experience anyway. I will be happy to see someone coming > up with a better definition and performance. GNUbg pathetic play in > many backgame situations leaves it open to abuse from humans. > > -Joseph > > On 9 February 2012 00:23, Mark Higgins <[email protected]> wrote: >> 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 <[email protected]> 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 >> >> >> >> _______________________________________________ >> Bug-gnubg mailing list >> [email protected] >> https://lists.gnu.org/mailman/listinfo/bug-gnubg >> > > _______________________________________________ > Bug-gnubg mailing list > [email protected] > https://lists.gnu.org/mailman/listinfo/bug-gnubg _______________________________________________ Bug-gnubg mailing list [email protected] https://lists.gnu.org/mailman/listinfo/bug-gnubg
