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Postby tso » Fri Feb 03, 2006 6:09 pm

QBasicMac wrote:
tso wrote:Also, Nikoli *defined* a Sudoku as...


Who the devil is "Nikoli"?

What if I *define* a Sudoku as a puzzle with a 1 in r1c1?

Mac


Nikoli is the Japanese company that coined the word "Sudoku". They have the copyright on the word within Japan. Before then, it was called "Number Place" -- a Dell Magazine puzzle that had no symmetry and generally had 36 givens. Nikoli made three changes -- 30 or less givens -- symmetrical placement -- made by hand.

It's their word. They have the right to define it.
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Postby QBasicMac » Fri Feb 03, 2006 7:38 pm

tso wrote:Nikoli is the Japanese company that coined the word "Sudoku".
It's their word. They have the right to define it.


OK. By definition, then. But still a puzzle that is not symmetric and has only one solution is still possible to solve with the techniques we have. The nuance is not the puzzle itself, but the definition of the word "Sudoku".

I just wanted to tell the OP that symmetry has nothing to do with puzzle solution methods.

I agree that symmetric puzzles are superior for the reason you gave: it helps locate errors when someone posts a puzzle incorrectly.

Cheers,

Mac
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none

Postby Chessmaster » Fri Feb 03, 2006 10:16 pm

yeah i now it stunk i will try to make a harder and better puzzle next time
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Postby MCC » Sat Feb 04, 2006 5:44 pm

TKiel wrote:When I entered Chessmasters' origional clues into Simple Sudoku it said it was asymmetrical. I thought I knew how to recognize symmetry in a puzzle and it seems to look symmetrical in his post, so I was just wondering where the asymmetricalness(?) occurrs. I could have made an error entering it, but I checked everything at least twice.

Tracy


Code: Select all
+-------+-------+-------+
| 5 . 8 | 2 . 4 | 6 . . |
| . . . | . 7 . | . . 4 |
| 3 . 4 | . 9 . | 5 . . |
+-------+-------+-------+
| 8 . . | . . . | . . 1 |
| . 9 . | 8 . 7 | . 2 . |
| . . 2 | . . . | 8 . . |
+-------+-------+-------+
| . . 5 | . 4 . | 1 . 6 |
| 6 . . | . 8 . | . . . |
| . . 3 | 9 . 6 | 7 . 5 |
+-------+-------+-------+

Offhand the grid Chessmaster posted may look symmetrical but the asymmetry arises in box 6 which should be like the following to have 180 degree rotational symmetry.

Code: Select all
+-------+-------+-------+
| 5 . 8 | 2 . 4 | 6 . . |
| . . . | . 7 . | . . 4 |
| 3 . 4 | . 9 . | 5 . . |
+-------+-------+-------+
| 8 . . | . . . | 8 . . |
| . 9 . | 8 . 7 | . 2 . |
| . . 2 | . . . | . . 1 |
+-------+-------+-------+
| . . 5 | . 4 . | 1 . 6 |
| 6 . . | . 8 . | . . . |
| . . 3 | 9 . 6 | 7 . 5 |
+-------+-------+-------+


I'm not sure if this a valid Sudoku.

MCC
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Postby TKiel » Mon Feb 06, 2006 2:52 pm

MCC,

You wrote
Offhand the grid Chessmaster posted may look symmetrical but the asymmetry arises in box 6 which should be like the following to have 180 degree rotational symmetry.


Is 180 degree rotational symmetry the same as the symmetry described in gsf's post
the top and bottom horizontal bands are symmetric on the diagonals
the middle horizontal/vertical bands are symmetric on the vertical

or are there different kinds of symmetry for the puzzles?

Tracy
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Postby MCC » Mon Feb 06, 2006 5:32 pm

TKiel wrote:Is 180 degree rotational symmetry the same as the symmetry described in gsf's post

Yes.

TKiel wrote:or are there different kinds of symmetry for the puzzles?

Tracy


I know of:
90 degree rotational symmetry
180 degree rotational symmetry
Diagonal symmetry
Symmetry about the horizontzl axis
Symmetry about the vertical axis

There may be other types and I'm sure someone will add to the ones I've mentioned if there are.

MCC
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Postby gsf » Mon Feb 06, 2006 5:51 pm

TKiel wrote:MCC,

You wrote
Offhand the grid Chessmaster posted may look symmetrical but the asymmetry arises in box 6 which should be like the following to have 180 degree rotational symmetry.


Is 180 degree rotational symmetry the same as the symmetry described in gsf's post
the top and bottom horizontal bands are symmetric on the diagonals
the middle horizontal/vertical bands are symmetric on the vertical

or are there different kinds of symmetry for the puzzles?

the point for this puzzle is that the top and bottom band symmetry is
incompatible with the middle band symmetry, which means that the puzzle
as a whole is not symmetric
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Postby tarek » Mon Feb 06, 2006 5:53 pm

MCC wrote:I know of:
90 degree rotational symmetry
180 degree rotational symmetry
Diagonal symmetry
Symmetry about the horizontzl axis
Symmetry about the vertical axis

There may be other types and I'm sure someone will add to the ones I've mentioned if there are.


Box Double reflection (which is also 180 symmetrical) (Combination of both Vertical & horizontal axes)
Triangle Double reflection (which is also 180 symmetrical) (Combination of both diagonal axes)

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Postby TKiel » Mon Feb 06, 2006 7:55 pm

Well, next time I guess I'll know better than to judge a puzzles symmetry by its looks.

Tracy

P.s. So any and all of the various types of symmetry could be used to set a 'symmetric' puzzle?
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