Talk:Sudoku/Archive 1

message: This archive page covers approximately the dates between Jan 1, 2005 and Sep 23, 2005.
Post replies to the main talk page, copying the section you are
replying to if necessary.  (See Wikipedia:How to archive a talk page.)
Please add new archivals to Talk:Sudoku/Archive 2. Thank you. angusj 23:05, 23 September 2005 (UTC)

message: The Sudoku puzzles printed in most UK newspapers are apparently computer-generated but employ symmetrical givens, implying a more humanistic algorithm;
::What!? Jooler 10:12, 14 May 2005 (UTC)
replies: text: I know "symmetrical givens" is defined in the article; "humanistic algorithm" (for the non-computer-scientists out there) means basically a computer program written to do something in the exact same way a human being would.  A computer could easily throw together a valid solution grid and then discard numbers to create a puzzle; I'm guessing Wayne Gould's program follows something more like the "Let's Make Sudoku!" site linked to by the article.  ...Anyone know Wayne Gould?  - ZM Zotmeister 17:50, 17 May 2005 (UTC)

text: Well when I wrote the above comment I hadn't read the term "givens" used in reference to numbers already placed in the grid, so it read as bewildering. I'm not sure "givens" is widely used anyway Google gives only 10 hits for 'sudoku +givens'. In any case the language is obscure. Jooler 10:35, 18 May 2005 (UTC)
replies: text: The term "given" (as a noun) is generic: it applies to many different kinds of puzzles, not just Sudoku.  It may also be the case that the term is only common parlance in the United States, whereas the Sudoku craze is presently epicentered in the United Kingdom.  ...Besides, this is an encyclopedia - this is where the terminology should be defined.  :)  - ZM  Zotmeister 16:18, 18 May 2005 (UTC)
replies: text: For what it's worth, I've become familiar with the term "givens" in this sense from UK-born puzzles, though my puzzle experience is wider than most. Hv 01:32, 17 August 2005 (UTC)
thread_title:  The term 'givens' 

message: Should these be trimmed a bit? A lot of it verges on link-spam. OpenToppedBus 12:17, May 24, 2005 (UTC)
I agree, but perhaps an interim measure would be to categorise the links. Poor quality links within each category could then be purged. JPF 13:00, 24 May 2005 (UTC)
thread_title: External links

message: I can't understand the following sentence? What is the matching involved? I can't see what the connection is between Sudoku and the Marriage Theorem. Dillon256 16:18, 25 May 2005 (UTC)
replies: text: The matching involved is related in principle to Hall's marriage theorem, in that the inductive method to prove Hall's theorem throws light on deductions to be made from any given set of restricted possibilities.
I've removed the sentence. Dillon256 13:17, 27 May 2005 (UTC)
thread_title:  Reference to Marriage Theorem 

message: ... funny. This seems to be a slightly more complex form of a test given to me as a psych evaluation for my current job. Oh, and I sucked at doing these :-) Ta bu shi da yu 06:45, 30 May 2005 (UTC)
thread_title:  Hmmm... 

message: What's with the italicisation? It's now entered English as a loanword, we don't need to italicise it.  Unless we want to italicise Chess . . . Slac speak up! 05:35, 2 Jun 2005 (UTC)
replies: text: I strongly disagree.  The italics distinguish it as a title of a published work, thereby properly reporting the current usage of the term.  We italicize (and capitalize) Sudoku and not chess for the same reason we emphasize Band-Aid brand adhesive bandages but not aspirin (which was once a registered trademark).  It is not the place of the Wikipedia to declare such a title generic, especially when it is still a very much active copyright; just because the copyright is not in an English-language-native nation is no excuse.  Even the original English name, Number Place, has remained unique to Dell for roughly three decades and has not become generic either.  - ZM  Zotmeister 18:53, 7 Jun 2005 (UTC)
replies: text: I think you may mean trade mark rather than copyright: in the UK, at least, there are so many different people publishing Sudoku puzzles, I doubt they are all licensing the term from the same person, any more than you would need to license the term "crossword" or "acrostic". -- ALoan (Talk) 18:17, 10 Jun 2005 (UTC)

text: In Japan, Sudoku is a registered trademark, and an enforced one, held by Nikoli.  Nikoli is now publishing their Sudoku puzzles in the UK, under the name Sudoku; although I don't know the precise legal details involved in their partnership with Puzzler Media, I think it is safe to say that Sudoku should not be assumed to be a generic term in any nation.  Removing its italics would be as ignorant as someone now moving this whole article to Number Place (something I almost did, albeit before the flood gates opened... and something that would still make empirical sense to me).  - ZM  Zotmeister 20:46, 10 Jun 2005 (UTC)
thread_title: Italics

message: No mention of Sudoku as a special form of Latin square? GraemeLeggett 08:27, 10 Jun 2005 (UTC)
replies: text: Strike that, small mention in middle of article. GraemeLeggett 08:34, 10 Jun 2005 (UTC)
thread_title:  LAtin squares 

message: I corrected the section regarding the NP-completeness of the problem. In fact the problem on 9 x 9 boards is finite and so trivial to solve with a Turing machine in constant time and space by walking the game tree and looking for a valid solution which uses the givens. The practical problem is that this constant is very, very large. The same issue exists with Chess, Checkers, and Go. Deco 22:21, 10 Jun 2005 (UTC)
thread_title:  NP completeness 

message: I'm not feeling brave enough to hack at a featured article but we have some duplications:
Para 1: "The aim of the puzzle is to enter a number from 1 through 9 in each cell of a grid, most frequently a 9×9 grid made up of 3×3 subgrids (called "regions"), starting with various numbers given in some cells (the "givens"). Each row, column and region must contain only one instance of each number."
Rules and term. 1st para: "The puzzle is most frequently a 9×9 grid made up of 3×3 subgrids (called "regions"). Some cells already contain numbers, known as "givens". The goal is to fill in the empty cells, one number in each, so that each column, row, and region contains the numbers 1 through 9 exactly once. Each number in the solution therefore occurs only once in each of three "directions", hence the "multiple isolations" implied by the puzzle's title."
History 3rd para: "He promoted the puzzle to The Times in Britain, which launched it on 12 November 2004. Three days later The Daily Mail began to publish the puzzle under the name "Codenumber"."
Pop. in newspapers 1st para: "The Times launched its regular Sudoku puzzle, introduced by Wayne Gould, on 12 November 2004. Three days later the Daily Mail began to publish the puzzle under the name "Codenumber"."
I think there was at least one more but I can't see them now. Secretlondon 08:55, 13 Jun 2005 (UTC)
thread_title: Repetitions

message: The article states that Sudoku was introduced in the Danish newspaper Politiken yesterday. I can't seem to find a reference, though. Could someone provide one?
On a related note, Morgenavisen Jyllands-Posten, which is published by the same company, started bringing Sudokus today. --Pidgeot (t) (c) (e) 15:34, 13 Jun 2005 (UTC)
replies: text: I can't find any references offhand, but they're on the back of section 1. And I'm going absolutely crazy over it. Maybe it's because I've been up for 24 hours, or maybe I've suddenly become daft, because I can't complete more than one number (for example get all 1s placed). After that I'm unable to figure out where to put anything else :) Mikkel 14:37, 20 Jun 2005 (UTC)
replies: text: Well, that's good enough of a reference for me :). --Pidgeot (t) (c) (e) 17:19, 20 Jun 2005 (UTC)
thread_title:  Sudoku in [[Politiken]]? 

message: Are there any views on why sudoku is so popular?  Here are some suggestions:-
#Self explanatory: it is easy to guess what to do merely by looking at the puzzle. 
#Convenient duration: the typical solving time corresponds to the duration of a commuter’s journey or a relaxation break. 
#Community: many other people are doing the puzzle providing a shared experience.
#Mental activity: many people enjoy mental activities which led to a clear conclusion:
##Puzzle solving: of those people who enjoy mental activities, many have a natural desire to solve problems.
##Satisfaction: completing puzzle gives sense of satisfaction. 
##Solving mental puzzles can be addictive.
#Self-esteem: completing puzzle confirms intelligence and reinforces self-confidence. 
##Self-deception:  difficult puzzles are avoided, failed puzzles are ignored.
#Egalitarian: solvers emphasise that a solution has been found rather the level of difficulty of the puzzle.
##The usually successful initial scanning process is not distinguished from the more difficult subsequent logical analysis process
#Prizes: some newspapers offer prizes for completing the puzzle.
JPF 12:37, 15 Jun 2005 (UTC)
thread_title: Psychology of sudoku

message: :Each number in the solution therefore occurs only once in each of three "directions", hence the "multiple isolations" implied by the puzzle's title.
I don't understand what this means -- could someone clarify? — Matt Crypto 14:11, 21 Jun 2005 (UTC)
replies: text: Each number in a solved Sudoku grid is the only one of its kind in its row - it's isolated, all alone.  It's also isolated in its column and isolated in its region.  - ZM  Zotmeister 15:53, 22 Jun 2005 (UTC)
replies: text:  Sorry, should have been more specific: I didn't understand the "multiple isolations" implied by the puzzle's title-bit. — Matt Crypto 21:55, 22 Jun 2005 (UTC)
replies: text:  That is a remnant of the wrong interpretation of the Japanese name, which was correctly deleted in this annonymous edit . --Pitan 22:35, 22 Jun 2005 (UTC)

text: Are you sure "number" for "multiple" wasn't an intentional pun?  - ZM Zotmeister 16:39, 23 Jun 2005 (UTC)
replies: text:  sū (数) never means "many" by itself, unlike the English expression "a number of". --Pitan 20:31, 23 Jun 2005 (UTC)
thread_title: "Multiple Isolations"

message: This section discusses what Sudoku-solving computer programs "would do", and what kind of programs "can be designed". Why not instead discuss what they "can do" and what "has been designed"? As it stands, it looks liks someone's speculation (it may be well-founded, but I can't tell). Fredrik | talk 11:53, 22 Jun 2005 (UTC)
replies: text: It's my work; I stand by its accuracy (download GNU Prolog, read the instructions on the FD constraint solver, and try it yourself if you don't believe me).  I'll try to tighten it up.  Solving a 9x9 properly-specified sudoku by computer is actually a fairly trivial problem and one, while I wouldn't inflict it on Introduction to Programming 101 students, I'd expect Algorithms 201 students to deal with in fairly short order. --Robert Merkel 15:04, 24 Jun 2005 (UTC)
thread_title:  Computer solutions section is poor 

message: I've found a method to generate sudokus which is extremely easy, although I have not found any reference to it in the web. Please feel free to use it.Just mention it as the "Peraita method". That'll make my mother very happy...
1. Generate a random permutation of the 1-9 digits. Let's take 123456789. But 298413765, or any other, would be perfect.
2. Assume that the 9 3x3 "quadrants" are named Q11, Q12, Q13, Q21, etc. according to their row.column placement. Each cell of each quadrant (81 in total) can be named as Q11-11, Q11-12, Q11-13... Q33-31, Q33-32, Q33-33.
3. Fill Q11 with "123456789", left-to-right, top-to-bottom. Thus, Q11-11=1, Q11-33=9.
4. Rotate-left "123456789" by one position, obtaining "234567891". Fill Q21 with that sequence: i.e. Q21-11=2, Q21-33=1.
5. Rotate-left the last sequence again, you'll get "345678912". Fill Q31; Q31-11=3, Q31-33=2.
6. Repeat this process with all 9 quadrants, going top-to-bottom and left-to-right. At the end, Q33-11=9, Q33-33=8.
7. I call the above procedure the "seeding" of the board. No matter what permutation of 1-9 you start with, you'll get a "valid" final board.
8. In the board you've just built many 3-long letter combinations are repeated, i.e. it is a very "obvious" board. You'll have to "shuffle" it. There are a number of "isomorphic" (that maintain the shape) transformations that you can use. Simmetries around the first diagonal (going from Q11-11 to Q33-33), the second diagonal (Q13-13 to Q31-31), the vertical axis (Q12-12 to Q32-12) and the horizontal axis (Q21-21 to Q23-23) are "global" transformations and I call them D1, D2, A1 and A2 respectively.
"Local" transformations consist of row or column swapping between two rows or columns belonging to one set of horizontal of vertical quadrants. Thus, columns 2 and 3 can be swapped, just as rows 4 and 6, for instance. All these transformations maintain the "validity" of the board.
These "shuffling" transformations can be applied in any number, in any order. You can force digists to move to designated places.
9. Now, you've got it! A beautiful filled-up Sudoku puzzle.
BREAK: I have a couple of questions here:
a. Can all valid sudoku boards be generated with the above algorithm?
b. Excluding repetition of three digit sequences (i.e. 345 or 678 appearing in more than one place), are some of the generated solutions intrinsically easier/harder than others? 
10. Aha!! Now comes the last process... That of transforming the solution into a problem. You'll do that by blanking ("prunning") some of the cells. But how many? When can you stop? How do you make sure you've not blanked one too many and created a multiple-solution problem? I'm still working on these issues. Any contribution will be welcome.
BTW: the above method works nicelly for boards of any n2 size.
:Hi there.  Wikipedia has a policy of No original research - Wikipedia is not intended to be the first place some new discovery or technique is published.  If you want to discuss new techniques for solving and composing sudoku, one place where there is an active discussion is at the forums on http://www.sudoku.com.  The discovery of the number of legal sudoku solutions came through discussion on those forums, for instance.  
:That said, one simple way of doing the "pruning" you describe in step 10 is to use a computer solver to check whether removing a cell makes the puzzle ambiguous.  --Robert Merkel 01:35, 13 July 2005 (UTC)
thread_title:  Building sodoku boards 

message: This is a good article, but I'm concerned about the large number of external links given. Wikipedia is not a web directory, and external links are chosen to be representative, rather than exhaustive. Can I suggest we trim the list down to just two or three of the best links in each case? — Matt Crypto 01:06, 15 July 2005 (UTC)
replies: text: Sure, but I think we need to decide which links are most useful, and lose most of the rest. We must easily have a hundred links in the "External Links" section (and that excludes the links in the "References" section) — that's well outside the norm for a Wikipedia article; I would think 10-15 ought to be plenty. One idea would be to link to directory sites, and then those sites can list every single newspaper with Sudoku, or the numerous solver software etc. — Matt Crypto 20:50, 16 July 2005 (UTC)
replies: text:  Should we not split off the content which relates to media coverage - popularity in newspapers, list of newspapers covering sudoku, internet pages etc., into a separate "Sudoku in the media" page? There is no doubt this latter page would expand in a variety of new forms e.g. TV programmes. JPF 12:06, 17 July 2005 (UTC)
replies: text: That sounds like a good idea to me, for one.  Keeping all the information while housecleaning the main article sounds like the best of both worlds.  - ZM Zotmeister 18:33, 17 July 2005 (UTC)
replies: text: Most annoying are the obvious ad links like this  one by 195.151.37.11 added under Solvers and helpers. Can I just rv this kind of edit by an anon with this being his first and only edit? hydnjo talk 16:13, 21 July 2005 (UTC)
replies: text: Never mind, I just boldly rv'd the ad link. hydnjo talk 02:25, 22 July 2005 (UTC)
thread_title:  External link explosion 

message: ... to find the "given" numbers in the last two columns in the "difficult" sudoku which used to be atop the Sudoku page. Part of this puzzle remains in older editions of the page, in the example (in red and green) of how to solve these.  I was working on it, and now it's disappeared, except for that partial reproduction. Thanks. I wanted to finish it on a flight tomorrow, to Canada to escape this dreadful D.C. heat. Sfahey 18:32, 22 July 2005 (UTC)
thread_title:  Help me, please ... 

message: The Daily Telegraph owned by Nationwide News Pty Ltd is the Sydney, Australia one. But does anyone know for sure that it is this one that is meant, not the London one? Barnabypage 21:11, 22 July 2005 (UTC)
replies: text: It clearly refers to the British Daily Telegraph in the second case (was rapidly introduced to several other national British newspapers including ...). It isn't obvious for the first reference (A three-dimensional Sudoku puzzle was invented by Dion Church ...). Hv 02:20, 17 August 2005 (UTC)
thread_title:  Which Daily Telegraph? 

message: 'Dell Number Place' is mentioned in the Construction section, but the reader will not know what that is, or why it is important, until the History section.
:Um... looks like it's covered in the intro paragraph to me.  - ZM Zotmeister 17:08, 26 July 2005 (UTC)
thread_title: Article disposition problem

message: OK, I'm still worried about the large number of external links, particularly as this is a Featured Article and shouldn't have these problems. It seems to me, after watching this page, that various software authors come and add their particular Sudoku app to the list -- and, given that it looks like a link directory, why wouldn't they? I've moved the somewhat dry lists of newspapers featuring Sudoku to a separate article, List of newspapers featuring Sudoku. To be cheeky and stimulate discussion, I've moved the external links here — let's add just the good ones back. Remember folks, Wikipedia is not a link repository ;-) — Matt Crypto 23:28, 2 August 2005 (UTC)
replies: text: The list is currently at Sudoku/Resources so there's no point having it here as well. --angusj 09:37, 9 August 2005 (UTC)
thread_title:  External link explosion 2 

message: John, I think a very brief entry concerning the Sky One fiasco is of general interest in that it demonstrates very well that Sudoku can be badly constructed and consequently have multiple solutions. I just don't think that details of the TV show is of sufficient interest to be included here too. Of course, this is only my opinion so I'm happy to open it to debate for you and others to comment. --angusj 15:11, 13 August 2005 (UTC)
replies: text: Angus, I personally find it interesting to see how sudoku (and other cerebral pastimes such as chess and bridge) are handled in the media - not just newspapers. To the extent that a TV programme has been attempted with little success then we have learned something. Perhaps there will be another TV format in the future which will strike a more fruitful vein.  The fiasco was the puzzle on the hill rather than the programme itself. Media is concerned about formats rather than the content of a puzzle. JPF 22:59, 13 August 2005 (UTC)
replies: text: Hi John. Yes, I agree the fiasco was the badly constructed 'puzzle on the hill', not the TV programme per se. I've come round to understanding and agreeing with your position that the TV programme is independantly of interest as Sudoku at that point entered a new media (even though from reports it was far from successful). Thanks for your patience,  I'm happy to restore your original edit. --angusj 23:26, 13 August 2005 (UTC)

text: Well I'm very confident your solver is wrong - see http://www.setbb.com/phpbb/viewtopic.php?t=179&mforum=sudoku. (My Simple Sudoku Program also agrees with Simes that there are 1905 solutions.) --angusj 22:36, 15 August 2005 (UTC)
thread_title: Popularity in the media

message: Recent addition by an anon:
: Although difficult at times, all puzzles can be solved without guessing numerical values.
That's not been my experience, and the Sudoku books I've read strongly imply that guessing is necessary for some tough puzzles. The statement is true in the strictest sense; for example, you could, in theory, build a large lookup table of Sudoku puzzles and simply look up the answer, but I don't think that's what's meant here. — Matt Crypto 13:41, 14 August 2005 (UTC)
replies: text: Yes, I agree it is premature to claim that all puzzles can be solved without guess. --angusj 14:11, 14 August 2005 (UTC)
replies: text: This reminds me of the anecdote of G.H.Hardy who left giving a lecture at Cambridge hesitating in mid thought only to return some time later to confirm that the point under consideration was indeed obvious. Sometimes it may be easier to take the guessing route than to think through an analytical solution. JPF 23:36, 14 August 2005 (UTC)
replies: text: Sad, but true.  There's what's deducible, and then there's what's reasonably deducible by a human.  The complexity of a Sudoku puzzle can exceed that, even if it has a unique solution.  Although any Sudoku with a unique solution can be solved through deduction alone, it is sometimes so tortuous [to use John Foley's word - I had actually meant 'torturous', by the way] that rolling out Ariadne's Thread actually becomes more efficient.  So although the statement is true for properly-built puzzles, I agree that its absence is desirable.  - ZM  (Zotmeister 14:50, 17 August 2005 (UTC)
thread_title: Guessing never necessary?

message: There seems to be some contention over whether the section on "magic Sudoku" is of any encyclopedic merit.  My personal opinion is that this "discovery" is perfectly trivial - swapping the digits of a puzzle so that the lo shu appears in it is of negligible difficulty and of no particular value.  I'm thinking it's self-aggrandization and am quite willing to delete the paragraph whole, but I'd like to see what others think of this.  - ZM (Zotmeister 14:50, 17 August 2005 (UTC)
replies: text: I agree, this is not sufficiently notable. — Matt Crypto 15:08, 17 August 2005 (UTC)

text: I also agree, not sufficiently noteworthy. --angusj 23:57, 17 August 2005 (UTC)
thread_title: "Magic" ''Sudoku'' a triviality?

message: "Dell Number Place puzzles are computer-generated... They also have no authoring credits."
"Dell Number Place Challenger puzzles also list author credits."
I would fix it, but I don't know which is correct :)
Captbaritone 00:00, 18 August 2005 (UTC)
replies: text: The first statement "computer-generated... have no authoring credits" is incorrect. The credits are directed to the copyright owner of the software that generates the puzzles. --angusj 23:52, 17 August 2005 (UTC)
replies: text:  I removed the "have no authoring credits" sentence. Captbaritone 00:22, 18 August 2005 (UTC)
replies: text: Ahem: Number Place and Number Place Challenger, as noted in the Variants section, are NOT the same puzzle - there is no inherent contradiction.  In addition, the article reads "credits", not "copyright notices" - the name of the constructor of an individual Number Place puzzle in a Dell magazine is NOT printed alongside the puzzle [presumably because it isn't a human]; the constructor of a Number Place Challenger IS.  What is meant is clear from the context of the rest of the section, which mentions Nikoli's listing of the author's name beside each puzzle.  I am reverting that edit.  - ZM Zotmeister 14:22, 18 August 2005 (UTC)
replies: text:  I'm not really fussed either way but I would consider a copyright notice a form of credit too, but it also has other legal meanings. --angusj 23:28, 18 August 2005 (UTC)

text:  What exactly is the difference beteen Number Place and Number place Challenger? and perhaps this difference could be pointed out in this section to avoide confusion. Thanks for your input. Captbaritone 01:06, 19 August 2005 (UTC)
replies: text: The difference is detailed under Variants, as I just said.  Article redundancy is frowned upon, but I can add "(see Variants)" after "Number Place Challenger" in the Construction section.  - ZM Zotmeister 15:45, 19 August 2005 (UTC)
thread_title: The section on Construction contradicts itself.