dailysudoku.com

[Marty R.]

Where does logic end and trial-and-error start? To me, that line seems blurred. It’s clear that techniques such as pairs, triples, etc., wings, fish, coloring, strong links, rectangles, and the like fall into the category of logic, but it’s the chains that have me wondering.

Suppose one decides to start a forcing chain based in a two-candidate cell. Or he sees that a number can occur only twice in a certain box and decides to test for each of the possible occurrences. It seems that the actions taken from these chains are based on logic; for example, cell such-and-such is “X” for either value, therefore, that cell must be “X.” But the deciding where to start these tests seems to have an element of trial-and-error to it, unless, of course, there is some sort of logic that tells one where to start the chain.

So where do YOU draw the line? How do you define trial-and-error? What does a puzzle constructor have in mind when he guarantees that his puzzles are all solvable by logic, without resorting to trial-and-error?

[TKiel]

[ravel]

Thanks Tracy,
you have formulated, how i think about it, much better than i could

[Marty R.]

Tracy, I agree with Ravel, I don't see anything wrong with what you say. But I do frequently see references to trial-and-error and am just trying to find out what people mean by it.

[David Bryant]

To me, "trial and error" means outright guessing -- just enter a value in some cell, and try to work the puzzle. If it works out, you're done -- if not, go back to the starting point and make another guess.

I think that Alan R is the only regular poster on this forum who wants to define forcing chains as "T&E". dcb

[keith]

The answer here is entirely subjective, an opinion. And, sometimes used to denigrate someone else's solution technique.

What David describes is called "backtracking".

An backtracking analog is to solve a maze: Unroll a ball of string to mark your path. Go anywhere. If you reach a dead end, back up to the last intersection (with your string), mark the passage as no good, and try any other unmarked path. Guaranteed to work, but most would agree this is trial and error.

Keith

[TKiel]