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unsolvable so far

 
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eckmann

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PostPosted: Wed Mar 22, 2006 11:22 am    Post subject: software, FAQ? Reply with quote

I have some logic-solver software in perl.

It can solve at least one of the problems on the page with "unsolvable so far"
sudokus (I think it is #3)

before getting excited, I would like to know whether those problems are really not solved by current logic-programs...
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Ruud
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PostPosted: Wed Mar 22, 2006 1:03 pm    Post subject: Reply with quote

I have split your post from the sticky at the beginning of this forum, as it is a separate question.

Could you please give us a link to the "unsolvable so far" sudokus you are mentioning?

Ruud.
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eckmann

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PostPosted: Wed Mar 22, 2006 1:08 pm    Post subject: logic... Reply with quote

http://www.sudokusolver.co.uk/grids_nologic.html


I am sorry, I dont know where to write to...

(if you wish, we can email privately, and only go "public" if I have anytthing t say...

J-P Eckmann
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Ruud
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PostPosted: Wed Mar 22, 2006 2:26 pm    Post subject: Reply with quote

Hi,

I checked the first 4 on that site. These are the puzzles and the techniques I used to solve them:

Code:
020000000000600003074080000000003002080040010600500000000010780500009000000000040
Naked & hidden Subsets, XY-Wing, Finned X-wing

300800000060479003004063070600001000005000100000200009090620400700948010000005002
Naked subset, BUG, finned X-Wing, Nishio + Forcing Chain

000005803007003150000060007600380070900000008030079006500030000089600200304200000
Naked subset, XYZ-Wing, 3 finned X-Wing, BUG

400080100100006705000900200009405602000000000601208300005009000806100009002060007
Naked pair, forcing chain


They are difficult, but not unsolvable.

Ruud.
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eckmann

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PostPosted: Wed Mar 22, 2006 3:36 pm    Post subject: Reply with quote

so where are problems which are currently "unsolved"?
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Ruud
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PostPosted: Wed Mar 22, 2006 5:29 pm    Post subject: Reply with quote

I think you are looking for something that does not exist. With backtracking, every Sudoku can be solved, or proven to be invalid (not having a single solution).

There are Sudokus, which require complicated implication chains to be solved. Some would consider those to be unsolvable, but with computer power, these can all be solved. Try some of the sudokus in this thread: http://www.setbb.com/sudoku/viewtopic.php?t=610&mforum=sudoku

The boundaries between solvable and (humanly) unsolvable sudokus is constantly shifting, as more and better solving techniques are discovered.

Ruud.
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eckmann

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PostPosted: Wed Mar 22, 2006 8:52 pm    Post subject: Reply with quote

no, I do (and did) understand all along. An interesting sudoku is one with only one solution which can be solved by logic alone (in particular, no backtracking).

Now, I consider a sudoku "unsolved" if no "published" algorithm can find its solution. some of these may need backtracking forever, and some will yield to new ideas. I agree that the boundary is ill defined, because saying a thing like
"if I do this,,, then that is impossible..." is in fact a form of backtracking. so the elegance of the rule is probably part of the quest.

Programming: Given an algorithm, I just write it down in perl, and check through any sudoku I am given. I discovered many of the rules with fancy names myself, and am willing to add the others to my program. once I have those, I want t check what remains non-solvable to check my ideas.

for this I need the list of tricks, XY,....

and lists of sudokus which are not solved by any given program. I was under the impression that the sudoku site has both of these...

so if you know where they are, thats all I need to know...
JPE
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Ruud
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PostPosted: Wed Mar 22, 2006 9:40 pm    Post subject: Reply with quote

This list of tricks can be found here: http://www.setbb.com/sudoku/viewtopic.php?t=379&mforum=sudoku

And an even bigger list can be found here: http://www.sudoku.com/forums/viewtopic.php?p=21804#21804

Ruud.
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