Sorry if this is a duplicate / not something allowed in here, I do not use the math section often.
I am looking for a word to describe something that cannot be calculated "backwards", once it is calculated "forwards". Maybe it is a relation of some sort?
One example might be found in cryptography I think, where, for example, when you calculate a compressed hash out of something, you cannot really calculate the original information back from the hash. What is that phenomenon called? Are there different words to describe something like that?
Perhaps you're looking for "non-reversible", which describes an operation which cannot be done in the reverse direction in a one-to-one fashion. The opposite will, of course, be that the operation is "reversible".