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project a sudoku whitout a computer

 
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profnassif

Joined: 13 Aug 2006
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PostPosted: Sun Aug 13, 2006 12:53 pm    Post subject: project a sudoku whitout a computer Reply with quote

Before computers, how to project a sudoku?
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mistermac

Joined: 03 May 2008
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PostPosted: Sat May 03, 2008 9:25 am    Post subject: Reply with quote

This is my first post, and I apologise if I am treading over well worn ground.

I also do not know the right place to put my first post, but seeing this one was almost empty, i thought I would use it!

I am an amateur mathematician, which means i do not have a degree which incorporates same, and am on old retired COBOL programmer, which makes me an amateur programmer also. I Have none of the current languages, which are i am sure very elegant and efficient.

From reading Wiki, and a few posts here, it seems that no one has ever provided a valid puzzle with less than 17 initial clues.

I am surprised that with so much computer power around, and so much effort, that if it were possible, that a 16 clue puzzle has not been found.

Without knowing any real theory, it seems to me in my present that state of knowledge that it is not possible. BUT, if taht were so, it would probably have been mathematically proven. So, I am probably wrong.

Can someone who knows the theory, please explain, if they can, why the hope is held out for a 16 or less sulution.

I was wrong many years ago, whwn i trie d to find out the shortest way to get 10 Chinese Checkers across a board with no opposing pieces, and found that my solution was 1 move short of the best possible.

Perhaps the same here.

A search for information theory has prompted my joining this Forum, as I feel Sudoku is a way to develop a larger theory of packing meaningful information as economically as possible.

Would Kelly, who helped developed the theory of overcoming the problem of more accurate data transmission over "noisy" communication lines be known to any members of the forum.

I was also interested to see that some of you try to generate Sudokus using raw random numbers as "seeds" in an attempt to make the whole problem more interesting.

Best!
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Adak

Joined: 27 Feb 2008
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PostPosted: Sat May 03, 2008 10:25 am    Post subject: Reply with quote

Hi Mac,

Best to just start a new thread, rather than "bring back" a 2 year old thread, to "life".

And "Welcome" to the forum. Smile

Glenn (gsf), amongst others, are doing a lot of testing to see if they can find all the 17 givens puzzles, and at the same time, checking many 16 givens puzzles, as well.

There is also a Sudoku Project on BOINC, but it's working from the 12's on up. Seems quite flawed to me.
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north55

Joined: 02 Dec 2006
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PostPosted: Sat May 03, 2008 6:07 pm    Post subject: Re: project a sudoku whitout a computer Reply with quote

profnassif wrote:
Before computers, how to project a sudoku?


If your question is on how to create a valid puzzle without a computer here is an answer.

Get some paper.

Mark out a grid with all candidates shown.

Code:
.---------------------------------.---------------------------------.---------------------------------.
| 123456789  123456789  123456789 | 123456789  123456789  123456789 | 123456789  123456789  123456789 |
| 123456789  123456789  123456789 | 123456789  123456789  123456789 | 123456789  123456789  123456789 |
| 123456789  123456789  123456789 | 123456789  123456789  123456789 | 123456789  123456789  123456789 |
:---------------------------------+---------------------------------+---------------------------------:
| 123456789  123456789  123456789 | 123456789  123456789  123456789 | 123456789  123456789  123456789 |
| 123456789  123456789  123456789 | 123456789  123456789  123456789 | 123456789  123456789  123456789 |
| 123456789  123456789  123456789 | 123456789  123456789  123456789 | 123456789  123456789  123456789 |
:---------------------------------+---------------------------------+---------------------------------:
| 123456789  123456789  123456789 | 123456789  123456789  123456789 | 123456789  123456789  123456789 |
| 123456789  123456789  123456789 | 123456789  123456789  123456789 | 123456789  123456789  123456789 |
| 123456789  123456789  123456789 | 123456789  123456789  123456789 | 123456789  123456789  123456789 |
'---------------------------------'---------------------------------'---------------------------------'


Pick a number and enter it wherever suits you.
Update the grid's candidates.

Code:
.---------------------------------.---------------------------------.---------------------------------.
| 12456789   3          12456789  | 12456789   12456789   12456789  | 12456789   12456789   12456789  |
| 12456789   12456789   12456789  | 123456789  123456789  123456789 | 123456789  123456789  123456789 |
| 12456789   12456789   12456789  | 123456789  123456789  123456789 | 123456789  123456789  123456789 |
:---------------------------------+---------------------------------+---------------------------------:
| 123456789  12456789   123456789 | 123456789  123456789  123456789 | 123456789  123456789  123456789 |
| 123456789  12456789   123456789 | 123456789  123456789  123456789 | 123456789  123456789  123456789 |
| 123456789  12456789   123456789 | 123456789  123456789  123456789 | 123456789  123456789  123456789 |
:---------------------------------+---------------------------------+---------------------------------:
| 123456789  12456789   123456789 | 123456789  123456789  123456789 | 123456789  123456789  123456789 |
| 123456789  12456789   123456789 | 123456789  123456789  123456789 | 123456789  123456789  123456789 |
| 123456789  12456789   123456789 | 123456789  123456789  123456789 | 123456789  123456789  123456789 |
'---------------------------------'---------------------------------'---------------------------------'


Pick another valid number in a cell that can provide symmetry and repeat until you have a valid puzzle, which you determine by checking to see what candidate eliminations can be done after each entry.

A valid puzzle will have symmetry and only one solution.

It is a lot of work!
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mistermac

Joined: 03 May 2008
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PostPosted: Wed May 07, 2008 4:47 am    Post subject: Reply with quote

Quote:
Pick another valid number in a cell that can provide symmetry


Thus says North55.

If you could, could you elaborate on what kind of, or where the symmetry is supposed to occur.

Before I die , I wish to create from scratch one valid unique solution Sudoku, with less than 50 clues. I am quite good at ones which provide 72 clues, but most people, not all, find them too easy!
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coloin

Joined: 05 May 2005
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PostPosted: Wed May 07, 2008 12:42 pm    Post subject: Reply with quote

I think north55 is trying to show you how to make a symmetrical puzzle [not essential IMO], perhaps confusing the making of the grid and the removal of clues.

There are two stages
1 make the grid [i believe you have done this already]
2 remove clues

Stage 1
Insert 25 clues into an empty grid. Keeping basic constraints in mind it is unlikely that there will be no solutions. Add clues carefully and with luck you will get a complete valid grid.
Stage 2
It is easy to get less than 50 clues straight off
Remove all clues from boxes 3,5,7.
Remove a single clue form all the remaining 6 boxes.
You will have a valid non minimal puzzle with 48 clues. Remove a good few more if you feel lucky.


It would be quite tricky to get down to a minimal puzzle by hand.

If you remove clues [from the solution grid already made in stage one] you have a 50 percent chance of a valid [non-minimal] puzzle around the 42 clue stage. The validity depends on all the clues hitting all the unavoidable sets in the complete grid. There are many > 10000. unavoidable sets in every complete grid.

If you insert clues into an empty grid [but use the solution grid made in stage one] you could quite easily make a puzzle with <35 clues.

C


Last edited by coloin on Wed May 07, 2008 1:54 pm; edited 1 time in total
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Jean-Christophe

Joined: 19 Mar 2006
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PostPosted: Wed May 07, 2008 1:26 pm    Post subject: Re: project a sudoku whitout a computer Reply with quote

profnassif wrote:
Before computers, how to project a sudoku?


See also: http://puzzle.gr.jp/show/English/LetsMakeNPElem/01
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Jean-Christophe
"When you have eliminated the impossible, whatever remains, however improbable, must be the truth." Sherlock Holmes.
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north55

Joined: 02 Dec 2006
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PostPosted: Thu May 08, 2008 2:52 am    Post subject: Reply with quote

coloin wrote:
I think north55 is trying to show you how to make a symmetrical puzzle [not essential IMO], perhaps confusing the making of the grid and the removal of clues.

There are two stages
1 make the grid [i believe you have done this already]
2 remove clues

C


No, I wasn't confused. I would never suggest a handmade puzzle being created by taking a complete grid and removing clues.

If you see newspaper puzzles published without symmetry, I will be surprised. I admit that it is an unneeded constraint.
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north55

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PostPosted: Thu May 08, 2008 2:59 am    Post subject: Re: project a sudoku whitout a computer Reply with quote

Jean-Christophe wrote:
profnassif wrote:
Before computers, how to project a sudoku?


See also: http://puzzle.gr.jp/show/English/LetsMakeNPElem/01


Very useful, although not likely to make a puzzle past easy. Great link!
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Jean-Christophe

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PostPosted: Thu May 08, 2008 8:37 am    Post subject: Reply with quote

There is also another page, but in Japanese only
Babelfish Translation
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Jean-Christophe
"When you have eliminated the impossible, whatever remains, however improbable, must be the truth." Sherlock Holmes.
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coloin

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PostPosted: Thu May 08, 2008 9:13 am    Post subject: Reply with quote

Apologies to north55 but mistermac appeared desperate to make a puzzle with less than 50 clues.

I agree inserting clues preferentially will tend to generate puzzles with slightly less clues - and it will be easier perhaps to add the final clues which define the solution.

Inserting clues from a predetermined grid will remove the chance of generating an invalid puzzle. You will always get a puzzle at the end - although it might have around 40 clues. It might even be symmetrical.

However i dont think it is worth trying to make a symmetric and minimal puzzle by hand.

C
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mistermac

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PostPosted: Fri May 09, 2008 8:56 am    Post subject: Reply with quote

Quote:
but mistermac appeared desperate to make a puzzle with less than 50 clues


Desperate is not a strong enough word.

It is now my whole raisin debt.

I will think of 25 single digit numbers, insert them with duplication of a number in rows, columns or little squares, hope I do not get a contradiction and solve till symmetry.

My puzzle will then be published here on this very thread, so get your pencils sharpened, and your erasers shaved!
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m_b_metcalf

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PostPosted: Mon May 12, 2008 12:00 pm    Post subject: Reply with quote

mistermac wrote:

It is now my whole raisin debt.


I don't think you owe anyone here any raisins. Or did you mean raison d'Ítre? Smile

Regards,

Mike Metcalf
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mistermac

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PostPosted: Tue May 13, 2008 8:15 am    Post subject: Reply with quote

I will have to look in my currant account to see if I owe anyone here.

Besides, I have trouble rolling my r's the way the French do.

BTW, the NYY's owe me a bit, can you do anything about that?

Meanwhile, I am plugging on with my Sudoku, I only hope it has only one solution.

Otherwise, I will have to settle for a Latin Square.
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