## Sudoku Explainer: Bugs, Quirks and Other Remarks...

Programs which generate, solve, and analyze Sudoku puzzles

### Re: Sudoku Explainer: Bugs, Quirks and Other Remarks...

There are two rather significant anomalies with Sudoku Explainer that I don't recall seeing discussed anywhere. If anyone knows of prior discussions, please post the appropriate link(s).

• Explainer has an xy-loop technique but no xy-chain technique. The "xy-loop" is a continuous nice loop that Explainer calls a "Bidirectional Y-Cycle." The "xy-chain" is a discontinuous nice loop.
• For the continuous nice loops that Explainer does find, it makes valid exclusions in rows, columns and boxes ... but makes no exclusions in cells. These cells are the junctions of two bilocal strong links that may occur in the continuous nice loop that Explainer calls a "Bidirectional Cycle."
ronk
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### Re: Sudoku Explainer: Bugs, Quirks and Other Remarks...

999_Springs wrote:

3. SE doesn't recognise "UR/UL Type 3 with Hidden Pair" if either of the two cells at the intersection of the UR/UL and the subset contain 5 or more candidates. That is SO STUPID. Type 3 with Hidden Pair only relies on two trilocations, regardless of numbers of candidates in each cell.

I have fixed this problem, anybody interested in this fixed version should either PM or post a request for that version
lksudoku

Posts: 90
Joined: 06 October 2010

### Re: Sudoku Explainer: Bugs, Quirks and Other Remarks...

ronk wrote:There are two rather significant anomalies with Sudoku Explainer that I don't recall seeing discussed anywhere. If anyone knows of prior discussions, please post the appropriate link(s).

• Explainer has an xy-loop technique but no xy-chain technique. The "xy-loop" is a continuous nice loop that Explainer calls a "Bidirectional Y-Cycle." The "xy-chain" is a discontinuous nice loop.
• For the continuous nice loops that Explainer does find, it makes valid exclusions in rows, columns and boxes ... but makes no exclusions in cells. These cells are the junctions of two bilocal strong links that may occur in the continuous nice loop that Explainer calls a "Bidirectional Cycle."

Nice to see people are adding to my compilation. I'll credit you with #81 and #82. I'm sure I had the second one down somewhere, but I must have been mistaken.
999_Springs

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Location: In the toilet, flushing down springs, one by one.

### Re: Sudoku Explainer: Bugs, Quirks and Other Remarks...

Another quirk of SE - which I thought I had read somewhere but couldn't find in this thread...

I accidentally tried to rate an invalid (multi-sol) puzzle. After quite some time - at least a minute or two - with me thinking I have a good puzzle here! - it gave a 20.x.x rating.

It would be good if it had a validity check at the start to avoid trying to rate them.
BryanL

Posts: 247
Joined: 28 September 2010

### Why is this not an Aligned Pair Exclusion ??

Why is this not an Aligned Pair Exclusion ("APE") for ER=6.2? Does Sudoku Explainer restrict the cells of an APE to a box and a line (row or column)? If "yes", is this restriction commonly applied by others?

Code: Select all
`..4..2..3....4..8.8..3..1....3.7...6.5.9...7.6.....5....9..7..8.1..9....2..4..6..At the point of the "Cell Forcing Chain (ER=8.3)" move:*159  *69    4     | 15678 1568  2     | 79   *56    3 135-9 2369  125   | 167   4     156   | 279   8     259 8     267   257   | 3     56    9     | 1     2456  245-------------------+-------------------+------------------*19    289   3     | 158   7     1458  | 2489  24    6 4     5     28    | 9     2368  36    | 38    7     1 6     2789  1278  | 128   1238  134   | 5     234   29-------------------+-------------------+------------------ 35    4     9     | 256   2356  7     | 23    1     8 7     1     6     | 28    9     38    | 234   2345  245 2     38    58    | 4     135   135   | 6     9     7r2c1 -9- r4c1 -1- r1c1( -9- r2c1) -5- r1c8 -6- r1c2 -9- r2c1 ==> r2c1<>9`
ronk
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### Re: Sudoku Explainer: Bugs, Quirks and Other Remarks...

Sudoku Explainer does not appear to restrict it's self to box line intersections, though the APE code is harder to read than average. SE does appear to restrict it's self to only using single cells with two candidates as excluding cells (ie does not use pairs of cells with three candidates between them).

The intersection of a box and a line definition for APE is in fairly wide use, see for example http://www.sudokuwiki.org/Aligned_Pair_Exclusion, or the rather poorly written Sudopedia definition.

JasonLion
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### Re: Sudoku Explainer: Bugs, Quirks and Other Remarks...

JasonLion wrote:Sudoku Explainer does not appear to restrict it's self to box line intersections, though the APE code is harder to read than average. SE does appear to restrict it's self to only using single cells with two candidates as excluding cells (ie does not use pairs of cells with three candidates between them).

SE does not implement APE type 2, only APE type 1 with two candidates excluding cells
lksudoku

Posts: 90
Joined: 06 October 2010

### Re: Sudoku Explainer: Bugs, Quirks and Other Remarks...

lksudoku wrote:SE does not implement APE type 2, only APE type 1 with two candidates excluding cells

So precisely what part of my example above makes it a type 2? Is it the <59> pseudo-pair in r1c28, the "pair of cells with three candidates between them" as JasonLion described?

BTW I think it's comical that a technique that almost no one uses has two types ... especially when the 2nd type 2 example on Andrew Stuart's web page is merely a naked triple.
ronk
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### Re: Sudoku Explainer: Bugs, Quirks and Other Remarks...

[Withdrawn and replaced with a later message.]
Last edited by daj95376 on Tue Nov 16, 2010 11:53 am, edited 1 time in total.
daj95376
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### Re: Sudoku Explainer: Bugs, Quirks and Other Remarks...

ronk wrote:
lksudoku wrote:SE does not implement APE type 2, only APE type 1 with two candidates excluding cells

So precisely what part of my example above makes it a type 2? Is it the <59> pseudo-pair in r1c28, the "pair of cells with three candidates between them" as JasonLion described?

The triplet 569 in r1c28 is an ALS with 3 candidates which could be used by APE type 2

And I am not certain that this case is considered as APE type 2, since in the description of it, it seems that both pair cells should see the triplet and in this case only one of the pair of cells sees the ALS
lksudoku

Posts: 90
Joined: 06 October 2010

### Re: Sudoku Explainer: Bugs, Quirks and Other Remarks...

Ron,

I ran the PM into my test SE replacement code and out popped an Aligned Triple:
Code: Select all
`\$ sudoku -bv < test.in -P004002003000040080800309100003070006450900071600000500049007018716090000200400697 puzzle 1 starting 159*      69*       4        |15678     1568      2        |79        +56       3 135-9*    2369      125      |167       4         156      |279       8         259 8         267       257      |3         56        9        |1         2456      245 --------- --------- ---------+--------- --------- ---------+--------- --------- --------- +19       289       3        |158       7         1458     |2489      24        6 4         5         28       |9         2368      36       |38        7         1 6         2789      1278     |128       1238      134      |5         234       29 --------- --------- ---------+--------- --------- ---------+--------- --------- --------- +35       4         9        |256       2356      7        |23        1         8 7         1         6        |28        9         38       |234       2345      245 2         38        58       |4         135       135      |6         9         7  1)  7.5 r2c1 <> 9 aligned triple in r1c1 r1c2 r2c1 + r1c8 r4c1 r7c1`

So my question is, "Even if it's not an APE, there's certainly an Aligned Triple lurking there, so why didn't SE pick the lower 7.5 scoring ATE???"

Cheers,
Paul
PIsaacson

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### Re: Sudoku Explainer: Bugs, Quirks and Other Remarks...

PIsaacson wrote:Ron,

I ran the PM into my test SE replacement code and out popped an Aligned Triple:
Code: Select all
`\$ sudoku -bv < test.in -P...  1)  7.5 r2c1 <> 9 aligned triple in r1c1 r1c2 r2c1 + r1c8 r4c1 r7c1`

So my question is, "Even if it's not an APE, there's certainly an Aligned Triple lurking there, so why didn't SE pick the lower 7.5 scoring ATE???"

Cheers,
Paul

What you describe is not ATE as in the link definition, I will quote the definition for APE, ATE is similar:
The Aligned Pair Exclusion can be succinctly stated: Any two cells aligned on a row or column within the same box CANNOT duplicate the contents of any two-candidate cell they both see.

In you example, for instance, r2c1 does not see r1c8 so this is not an ATE definition, at least according to the link description or SE computation
lksudoku

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Joined: 06 October 2010

### Re: Sudoku Explainer: Bugs, Quirks and Other Remarks...

[Withdrawn and replaced with a later message.]
Last edited by daj95376 on Tue Nov 16, 2010 11:54 am, edited 2 times in total.
daj95376
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### Re: Sudoku Explainer: Bugs, Quirks and Other Remarks...

daj95376 wrote:Paul has already demonstrated here that SE does not adhere to this definition of APE.

The only difference between the link definition and SE definition is that the SE pair can be any pair of two cells, not necessarily in the same row/column/box. However the requirement that the excluding cell will see both pair cells is maintained by SE according to the code and the above example
lksudoku

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Joined: 06 October 2010

### Re: Sudoku Explainer: Bugs, Quirks and Other Remarks...

lksudoku wrote:
daj95376 wrote:Paul has already demonstrated here that SE does not adhere to this definition of APE.

The only difference between the link definition and SE definition is that the SE pair can be any pair of two cells, not necessarily in the same row/column/box. However the requirement that the excluding cell will see both pair cells is maintained by SE according to the code and the above example

Often the "pivot cell" is an "excluding cell" too and then the "aligned pair", i.e., the pivot cell and the target cell, must obviously be in the same unit (row/col/box).
ronk
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