MrMind comments on Defining causal isomorphism - Less Wrong

1 Post author: badtheatre 14 December 2013 06:39PM

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Comment author: MrMind 16 December 2013 09:43:17AM 0 points [-]

Let's start small. Since we are talking about algorithms (better yet, about programs of a universal Turing machine), what about if two programs can match the same input on the same output?
Would that suffice as a definition of isomorphism, even if they have wildly different resource usages (including time)?

Comment author: badtheatre 17 December 2013 07:48:42PM 0 points [-]

What if they don't output anything?

Comment author: Baughn 16 December 2013 03:26:30PM *  0 points [-]

Sadly, even that is unprovable - I believe there's a way to convert a solution for this problem to one for the halting problem.

Of course you can still do it for a large fraction of functions you're likely to see in real life.

Comment author: asr 16 December 2013 03:56:01PM *  0 points [-]

Yes -- It's not possible to decide, given two programs, if they have identical behavior. I think that's okay here -- the original poster asked for a definition of equivalence, not for a definition that was always decidable.