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Sudoku Analyzer Bug Report
Fri February 14 2020  2:15pmSudoku

This Sudoku puzzle has me scratching my head.

The Sudoku Analyzer solves it step by step, giving clues along the way. Which is to say, it is not one of those occasional Sudokus which can only be solved in trial-end-error guesswork manner. But at a couple points, the Sudoku Analyzer gives very complex hints where simple hints are possible. This is not according to design. Then, in at least one very complex hint, several secondary hint steps are omitted, without which the complex hint is incomplete.

What's especially baffling is that these problems seem to be unique to the grid pictured. Other Sudokus, even much more complex ones, are still solved quite methodically, logically, and correctly. What's different about this particular Sudoku?

This blog post is a heads up. If you have encountered similar symptoms in other Sudokus, or if you have any insight into what's going on with this one, I would appreciate a heads up from you in return.

15 Feb 2020 Note:
Have fixed (I think) the second problem mentioned above, in which secondary hint steps were omitted. Sometimes just need a good night's rest to see things with fresh eyes. Still have to address the first, less serious problem, in which simple hints are passed over in favor of more complex hints. Stay tuned.

21 Feb 2020 Note:
Have done little to address the aforementioned problem of giving overly complex hints. For one thing, this appears to be an oddity that occurs quite rarely, and, as noted above, is not a serious bug. Furthermore, upon studying it, it seems to be inextricably linked to the inherent complexity of Sudoku itself. I may write a longer article or web page examining this interesting phenomenon. Right now, am declaring this report closed, the bug resolved.

22 May 2020 Note:
Recently encountered and fixed another, unrelated bug in the Sudoku Analyzer, a very difficult bug to track down. Briefly, it involved an occasional, random failure of the server-side binary executable due to its failure to properly align the stack pointer prior to calling a C function from an assembly routine, as is required on the 64 bit BSD server. Am sure everyone reading this understands exactly what this involves. ;)

Anyway, it's worth mentioning here because the long process of troubleshooting and correcting the random binary bug exposed another much less serious anomaly, which, now corrected, results in avoiding, in at least some advanced Sudokus, the above mentioned oddity of overly complex hints. But only in some cases. As the previous note also mentions, the apparent simplicity of Sudoku masks an inherent complexity that may be impossible for human brain nor computer program to fully master.

rev. Fri May 22  7:59pm
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rev. 2020.09.23