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Re: [Bug-gnubg] crashed position

From: Joseph Heled
Subject: Re: [Bug-gnubg] crashed position
Date: Thu, 9 Feb 2012 12:08:54 +1300

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.


On 9 February 2012 00:23, Mark Higgins <address@hidden> 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 <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
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