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I was mainly trying to point out that the mathematical term "computation" is not limited to deterministic computers. Since the GP was mentioning computable func
by tsimionescu 3y ago
I was mainly trying to point out that the mathematical term "computation" is not limited to deterministic computers. Since the GP was mentioning computable functions as something requiring determinism, I believe they were also talking more about the mathematical notion of computation rather than physical computers.
I should also note that our computers can very much solve NP-complete problems. They can't implement NP-complete algorithms to solve them, but all NP problems can be solved by a deterministic computer or a quantum computer - it just takes [much] more compute time (assuming P != NP, otherwise it may even take the same time).
This is very relevant to this discussion, because in fact it is well known and proven that the non-determinism in the NP model does not give any amount of extra computational power beyond a Turing machine. That is, a non-determinstic Turing machine can solve exactly the same set of problems as a deterministic Turing machine (but, as far as it is known today, faster). The same is true of Quantum computers.
Hyper-computation refers to even more fanciful mathematical models which are actually able to solve problems that a Turing machine can't solve, even with infinite time. They involve things like performing an infinite amount of Turing machine steps in one Hyper-Turing machine step, or having access to an oracle which tells you if a computation halts etc.
- btilly 3y agoYes, you can have fanciful "models of computation" with oracles of various kinds. Few people really think of that as computation. But I agree that there are real examples of physically possible computation which are not deterministic. The most widely used being true random number generators. And so theoretical computability is not necessarily the right model for the real world.
- tsimionescu 3y agoNote that analyzing the complexity of problems in relation to various oracles is probably half of computer science. Algorithms like those in NP are not exotic concepts, they are the bread and butter of many computer science courses and careers. Hyper-computation is much more exotic, though, I'll give you that.
- mjburgess 3y agoRandom number generation, if physically non-deterministic, isnt computation. https://en.wikipedia.org/wiki/Computable_function https://en.wikipedia.org/wiki/Computable_function