irreversible
irreversible
Any non-invertible function is "irreversible"
.
Lots of things are one-way. You could simply take a number, multiply by zero, and then ask someone to retrieve the original number. But, more to your point:
Ankur
The trignometric functions are irreversible if you use them over the domain of real numbers. For example, if you look at the sine function, you will find that f(x) = f(x + 2*k *pi) for all integer values of k.
trig
A more proper word for this is one-to-one, don't you remember your high school algebra and the "horizontal line test"?
Roose
Any function where a loss of information occurs. More exactly, any single operation where a loss of information occurs within a given context.
Holger
Ehm... XOR is reversible! since:
Matt
Google on "NP Complete"
Philo
What the hell does NP completeness have to do with a function being one-to-one?
Roose
format c:
TomA
Isn't NP completeness about being able to traverse an operation in either direction with equal ease?
Philo
Its been a long time since the computing theory lectures, but I though NP vs P was about whether you could find the *optimal* solution to a problem with a polynomial time algorithm (vs an exponential one). Classic case is the travelling sales man problem.
Rob Walker
and I mean domain, not range. doh.
Matt
Thats one of the differences in computers vs math.
The Artist Formerly Known as Prince
Rob - that's the point. The optimal solution *is* "the" solution. And there's no easy way to find it. But once you've found it, it's trivial to prove that it's the right answer.
Philo
Brush your twice a day and you will have your answer ;)
KayJay
Actually, Philo, a hash function is irreversable since it involves a loss of information.
Eudoxus
Then I'd have to clarify both the question and the answer...
Philo
> Rob - that's the point. The optimal solution *is* "the"
Rob Walker
> BTW, given this issue, doesn't that make addition
Rob Walker
It's not so much that you can only work with one unknown. An operation is reversible if it is one-to-one (or one-to-many but one-to-many mappings aren't too useful in this context). f(a,b) = a + b is not one to one so it is not reversible but if b is constant then f becomes one-to-one and is reversible even if we don't know anything about the constant's value.
Eudoxus
Thank you all for your feedback. I am too familiar with the technical terms but what I meant by "irreversible" is any operation that is hard to trace back. A one-way hash works nicely since it does a many-to-one kind of mapping. Trig functions work nicely too since they are periodic.
irreversible
No, I think you are conflating two distinct ideas.
Roose
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