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RE: [Bug-gnubg] Optional redouble, or is it automatic
From: |
Ian Shaw |
Subject: |
RE: [Bug-gnubg] Optional redouble, or is it automatic |
Date: |
Mon, 9 Sep 2002 14:20:20 +0100 |
> -----Original Message-----
> From: Joern Thyssen [mailto:address@hidden
> Sent: 09 September 2002 13:28
> To: Jim Segrave
> Cc: Ian Shaw; GnuBg Bug (E-mail)
> Subject: Re: [Bug-gnubg] Optional redouble, or is it automatic
>
>
> On Mon, Sep 09, 2002 at 01:19:57PM +0200, Jim Segrave wrote
> > On Mon 09 Sep 2002 (11:10 +0100), Ian Shaw wrote:
> > > Why is this type of position called an "optional
> redouble"? Surely the
> > > redouble is automatic. I guess the 2-ply analysis is
> looking ahead and
> > > automatically doubling on the next roll so it sees no
> loss of equity.
> > >
> > > GNU Backgammon Position ID: 2W4AAGdsbRMBGA
> > > Match ID : AgGgAAAAEAAA
> >
> > Odd - using today's build with evaluation set to world-class++ for
> > chequer and cube play I get the following evaluation:
> >
> > No redouble : +1.201
> > Redouble, take : +1.347 (+0.146)
> > Redouble, pass : +1.000 (-0.201)
> >
> > Correct cube action: Too good to redouble, pass
> >
> > Which, to my untrained eye looks far more reasonable.
>
> O is on roll... 15% looks reasonable with 2 chequers on the
> bar. Did you
> reverse the position to get X on roll?
>
Just to clarify the position:
GNU Backgammon Position ID: 2W4AAGdsbRMBGA
Match ID : AgGgAAAAEAAA
+-1--2--3--4--5--6-------7--8--9-10-11-12-+ O: mlp (Cube: 4)
| X O O O O | | O O O | 0 points
| X O O O | | O O | On roll
| X | | |
| | | |
| | | |
| |BAR| |^ 5 point match
| | | |
| | | |
| X | | |
| O X X X X | X | |
| X O X X X X | X | O | 2 points
+24-23-22-21-20-19------18-17-16-15-14-13-+ X: ian
This position is ID is actually bG0TARjZbgAAZw on my display. The score and
cube positions are correct, but the chequer positions are reversed. I have
two chequers back behind a solid four-prime. My opponent has three on the
two point and two on the bar.
Uncharacteristically I am behind in my updates and this is Oystein's
20020814 build, so this may be fixed by now.
The correct position is this:
+-1--2--3--4--5--6-------7--8--9-10-11-12-+ O: ian
| X O O O O | | O O O | 2 points
| X O O O | | O O |
| X | | |
| | | |
| | | |
| |BAR| |^ 5 point match
| | | |
| | | |
| X | | |
| O X X X X | X | | On roll
| X O X X X X | X | O | 0 points
+24-23-22-21-20-19------18-17-16-15-14-13-+ X: mlp (Cube: 4)
Reconsidering my original reason for posting, Os takepoint is at 75% (W-H
MET) because he can drop to Crawford 3-away. Nis is correct to argue that X
might drop incorrectly in future so holding on to the cube is OK. I'm not
sure that a bot sees this though since it assumes correct play by both
sides. In that case the only drops you get are correct drops because O has
lost his market, and therefore O wishes he had doubled earlier.
Ian