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Re: [Bug-gnubg] crashed position
From: |
Mark Higgins |
Subject: |
Re: [Bug-gnubg] crashed position |
Date: |
Fri, 10 Feb 2012 05:42:15 -0500 |
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: address@hidden [mailto:address@hidden On Behalf Of Joseph Heled
> Sent: 08 February 2012 23:09
> To: Mark Higgins
> Cc: address@hidden; 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 <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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