I haven’t followed the recent disucssion quite closely enough, I’ll give it more time eventually. At the moment, my solver is undergoing a radical revision. But, one pruning operation I’ve had for quite a while is the prevention of a->b->c type moves. Your 2-step (both irreversible) moves fall into that category. At step 1, you may have the option of moving a->b or a->c. If you select a->b, and have to back up because it didn’t work out, you prune b->c and back up to the a->c move. This appears to me to avoid the problem you encountered, and it avoids a lot of redundant moves. My solver looks back deeply to avoid these moves, they don’t have to be in sequence.
From: Shlomi Fish
Sent: Tuesday, August 14, 2012 6:14 AM
To: fc-solve-discuss_at_yahoogroups.com
Subject: Consistent Count of Irreversible Moves
Hi all,
after I had implemented the scheme I thought of in this post -
http://tech.groups.yahoo.com/group/fc-solve-discuss/message/1135 -
I found out that the new depth_dbm_fc_solver traversed more boards than
the normal dbm_fc_solver for one of the impossible deals. That indicated
that some deals were probably counted twice, so I decided to investigate.
What seems to have been the problem is the fact that some irreversible moves
actually consist of two irreversible moves. I.e: if we move the 2H from its original
location under a non-parent card to the foundations, then it would be equivalent to two
irreversible moves, because we may reach this in a different case by first moving it into
a freecell (one irreversible move) and then moving it to the foundation (another
irreversible move). So I need to account for those in both the calculation of the
rank of irreversibility of a single move, and the number of irreversible moves performed
by the Horne's Prune's process.
After I fixed this problem, the number of derived states and their contents was identical
between the depth_dbm_fc_solver and the dbm_fc_solver.
Regards,
Shlomi Fish
--
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Shlomi Fish http://www.shlomifish.org/
Interview with Ben Collins-Sussman - http://shlom.in/sussman
If God exists and is the ego‐maniacal, sadistic and helpless creature that is
described in the Old Testament, then we’re in deep trouble.
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Received on Wed Aug 15 2012 - 07:45:52 IDT