FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in          Games  Calendar Log in to check your private messages    How to visualize forcing chains Goto page 1, 2  Next          Sudoku Programmers Forum Index -> Solving sudoku View previous topic :: View next topic   Author Message Henk Joined: 13 Nov 2005 Posts: 105 : Items Posted: Wed Feb 01, 2006 12:03 pm    Post subject: How to visualize forcing chains I am expirimenting in my sudoku program on how to visualize a forcing chains hint. The best I can come up with is the following: Anybody has a better idea? Or is there a program that gives a understandable visual hint on forcing chains? _________________ Generate and solve Sudoku puzzles with Into Sudoku! Back to top Graeme Joined: 31 Jan 2006 Posts: 22 : Location: Adelaide Items Posted: Thu Feb 02, 2006 9:55 am    Post subject: Hi Henk, I really like the graphical presentation of your hints! If I understand this example, it leads to the removal of {9} candidate in C2. The Sadman definition http://www.simes.clara.co.uk/programs/sudokutechnique7.htm of Forcing Chains is: Quote: Forcing chains is a technique that allows you to deduce with certainty the content of a cell from considering the implications resulting from the placement of each of another cell's candidates. (This technique is also know as "double-implication chains".) So using this definition, Forcing Chains is about setting a value, and not about candidate removal. I have a technique I've called Forcing Chain Reduction that does what your example shows. Back to top Henk Joined: 13 Nov 2005 Posts: 105 : Items Posted: Thu Feb 02, 2006 10:07 am    Post subject: Quote: So using this definition, Forcing Chains is about setting a value, and not about candidate removal. I have a technique I've called Forcing Chain Reduction that does what your example shows. I was looking for the name of it, thanks! I did make a difference between the two, but I thought it was the same technique. I allways prefer setting a value over candidate removal in my program. _________________ Generate and solve Sudoku puzzles with Into Sudoku! Back to top Graeme Joined: 31 Jan 2006 Posts: 22 : Location: Adelaide Items Posted: Thu Feb 02, 2006 11:17 am    Post subject: I should point out that Forcing Chain Reduction is just a name I created for this variation of the Forcing Chain definition. Back to top angusj Site Admin Joined: 18 Jun 2005 Posts: 406 : Items Posted: Thu Feb 02, 2006 12:25 pm    Post subject: Graeme wrote: So using this definition, Forcing Chains is about setting a value, and not about candidate removal. No, Forcing Chains is about either. For examples see - http://www.sudoku.com/forums/viewtopic.php?p=9266#9266 http://www.sudoku.com/forums/viewtopic.php?p=10636#10636 Back to top Graeme Joined: 31 Jan 2006 Posts: 22 : Location: Adelaide Items Posted: Thu Feb 02, 2006 12:58 pm    Post subject: thanks, angusj It gets messy when there are different definitions of the same technique. Hard to know whether a definition is evolving, incomplete, old or embellished. Back to top Henk Joined: 13 Nov 2005 Posts: 105 : Items Posted: Fri Feb 03, 2006 7:12 pm    Post subject: angusj: Thanks for clearing that up... _________________ Generate and solve Sudoku puzzles with Into Sudoku! Back to top Graeme Joined: 31 Jan 2006 Posts: 22 : Location: Adelaide Items Posted: Sat Feb 04, 2006 2:20 am    Post subject: Does anyone know if there's an agreed documentation of solve techniques? Clearly, the Sadman site and the forum message linked above are at odds over what Forcing Chain includes. It seems that anyone, including me, can make up anything we like. Back to top angusj Site Admin Joined: 18 Jun 2005 Posts: 406 : Items Posted: Sat Feb 04, 2006 5:22 am    Post subject: Graeme wrote: Does anyone know if there's an agreed documentation of solve techniques? There isn't one. While there's consensus over naming perhaps the majority of techniques, there are a number of techniques where there's still no consensus (eg http://www.sudoku.com/forums/viewtopic.php?p=17388#17388). Also, newcomers sometimes add to the confusion by creating their own names (which is understandable since it's hard to find good documentation especially for existing but perhaps more 'exotic' techniques). Back to top Graeme Joined: 31 Jan 2006 Posts: 22 : Location: Adelaide Items Posted: Sat Feb 04, 2006 6:58 am    Post subject: I'm not surprised, Angus And yes, that's me; a newcomer with my own naming conventions, although I still think my Error Chains technique is not covered elsewhere. Funny thing, how you approach a technique as a programmer vs approaching it as a human lead you to different conclusions about how to classify techniques. That's how I found my Error Chains, by modifying my program to do the sorts of things a human would do. Back to top foxglove Joined: 04 Feb 2006 Posts: 42 : Location: Portugal Items Posted: Sun Feb 05, 2006 1:37 pm    Post subject: Re: How to visualize forcing chains Henk wrote: Anybody has a better idea? Or is there a program that gives a understandable visual hint on forcing chains? I gave up the very detailed explanations, let the user have fun sorting things out: So i cannot say that it gives a understandable visual hint on forcing chains! but well... Back to top fermat Joined: 05 Feb 2006 Posts: 25 : Location: Melbourne Items Posted: Sun Feb 05, 2006 7:49 pm    Post subject: Re: How to visualize forcing chains Henk wrote: I am expirimenting in my sudoku program on how to visualize a forcing chains hint. The best I can come up with is the following: Anybody has a better idea? Or is there a program that gives a understandable visual hint on forcing chains? I think that red lines to and from the square highlighted yellow should be a different colour, or should not be there as they are not (in my view) part of the chain. If you are willing to get even more detailed, given that some of the boxes in the chain might have more than just two candidates, perhaps you could colour the candidates directly involved as well. Back to top Henk Joined: 13 Nov 2005 Posts: 105 : Items Posted: Fri Feb 17, 2006 6:55 pm    Post subject: I implemented this: you like it? It was a real pain to implement manual drawing for this.. _________________ Generate and solve Sudoku puzzles with Into Sudoku! Back to top foxglove Joined: 04 Feb 2006 Posts: 42 : Location: Portugal Items Posted: Fri Feb 17, 2006 9:07 pm    Post subject: Henk wrote: you like it? Much clearer then coloring the background! It's a bit puzzling your missing half the steps. I have a little problem with the technique and your two colors for the lines show it: practically everytime there is more than one start! I had to remotely edit my post above because the original pict got lost, so now it's redone with your puzzle. There are 3 or 4 starts that make a forcing chain in the same chain of implications. What I'm I misssing here? Back to top Henk Joined: 13 Nov 2005 Posts: 105 : Items Posted: Fri Feb 17, 2006 9:29 pm    Post subject: foxglove: It took some time for my to figure out what your hint is doing, but now I undestand! I also see the difference, you color all 'candidates' for the chain. My hint shows just one path. They just are two different approces of giving the hint. I like the concept of showing all possible chain candidates. But I'm currious, how do you mark the value as the chains use the same candidate from the same cell, like these puzzles. Just give the candidate one color won't do then... First (triple implication chain): Code:  . . 5 | 7 . . | 9 . .  . . . | . 9 . | 7 . 3  7 9 . | . . 3 | 5 . 1 -------+-------+------  . . . | . 2 8 | 1 9 .  . . 9 | 4 . . | . 3 .  . 8 . | . . 9 | 4 5 . -------+-------+------  8 5 3 | 9 . . | . 1 4  9 . . | . 3 . | . 7 5  1 7 2 | . 5 4 | 3 . 9  234  1234 5    | 7    48   16   | 9    24   68   246  246  1468 | 1256 9    56   | 7    2468 3     7    9    468  | 26   48   3    | 5    246  1    ----------------+----------------+----------------  3456 346  467  | 356  2    8    | 1    9    67   256  126  9    | 4    167  57   | 68   3    28   236  8    167  | 36   16   9    | 4    5    27  ----------------+----------------+----------------  8    5    3    | 9    67   267  | 26   1    4     9    46   46   | 18   3    12   | 28   7    5     1    7    2    | 68   5    4    | 3    68   9    or this (triple implication chain): Code:  . 5 . | . 3 . | . . 2  3 7 . | 5 . 2 | . . 6  6 2 1 | . 9 . | 3 . 5 -------+-------+------  . 4 . | . . 8 | . 2 .  . . 3 | 9 . . | 5 . .  . 6 . | . 5 . | 7 . . -------+-------+------  . 3 . | 1 . 9 | 8 . .  . 9 . | 4 . 3 | . . .  . . . | . . 5 | . 3 .  489   5     489   | 678   3     16    | 149   14789 2     3     7     489   | 5     14    2     | 149   489   6     6     2     1     | 78    9     47    | 3     478   5    -------------------+-------------------+-------------------  579   4     579   | 37    16    8     | 169   2     139   27    18    3     | 9     24    67    | 5     16    48     1289  6     289   | 23    5     14    | 7     49    3489 -------------------+-------------------+-------------------  2457  3     24567 | 1     267   9     | 8     456   47     12578 9     25678 | 4     2678  3     | 126   156   17     1478  18    24678 | 26    2678  5     | 1249  3     1479 _________________ Generate and solve Sudoku puzzles with Into Sudoku! 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