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A visual proof that neural nets can approximate any function

neuralnetworksanddeeplearning.com

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Re: A visual proof that neural nets can approximate any function

#51
post #21
post #18

Can neural networks solve the halting problem?

No. Neural networks are still computed on Turing machines, which are mathematically proven to not be able to solve the halting problem.

If you are referring to our modern computers then they are actually computed on finite state machines - just with a lot of states. After all a Turing machine requires unbounded memory.

Re: A visual proof that neural nets can approximate any function

#52

Approximate, not compute. The function also must be continuous. NNs are good for approximation / interpolation / extrapolation, which makes them quite useful for certain domains of problems. But of course, it does not make them a kind of universal computing machine (in the computability sense, like universal Turing machines).

> NNs are good for approximation / interpolation / extrapolation Extrapolation? I was under the impression that generalizability of NNs beyond the training data was one of the major problems faced by NNs.

When they don't generalize well it usually means you have over trained on your training data. When you take classes on this stuff they have whole sections that talk about trying to detect this and what to do about it e.g. regularization, better models, more training data etc.

Re: A visual proof that neural nets can approximate any function

#53
post #47

Approximate, not compute. The function also must be continuous. NNs are good for approximation / interpolation / extrapolation, which makes them quite useful for certain domains of problems. But of course, it does not make them a kind of universal computing machine (in the computability sense, like universal Turing machines).

Wait a minute, isn't it also the case that according to the Weierstrass approximation theorem any continuous function on a closed interval can be approximated by a polynomial function? And isn't that kind of pointless for practical applications because we also need to avoid overfitting? To clarify, I'm not trying to make a snippy remark, I just happened to have used polynomial curve fitting before and looked up the W…

Yes, the claims are pretty much in the same spirit. Although the first (Weierstrass's) theorem [1] was stated for real-valued functions in a 1-D closed interval [a, b], Stone-Weirstrass is a generalisation of the above theorem [2] that's applicable in more general scenarios. Here is the formal statement:

- [1] http://mathworld.wolfram.com/WeierstrassApproximationTheorem...

- [2] http://mathworld.wolfram.com/Stone-WeierstrassTheorem.html

Neural Networks use a different "basis" (sigmoid, ReLU, etc.), but the underlying idea shares the same spirit.

Re: A visual proof that neural nets can approximate any function

#55
post #35

Skimming through the article, I understand that the author... A) was focusing on functions that take a certain amount of input variables and B) that the function (that s/he mirrored using the neural net) computes out of it directly one or more of result(s). C) To do that s/he used a backpropagation network (which is the only model I know very well). Right or wrong? EDIT: when I say "directly" I mean that the function…

I just got a downvote => I think that it's not fair to downvote a question, especially without posting the reason for the downvote :(

Re: A visual proof that neural nets can approximate any function

#57
post #47

Approximate, not compute. The function also must be continuous. NNs are good for approximation / interpolation / extrapolation, which makes them quite useful for certain domains of problems. But of course, it does not make them a kind of universal computing machine (in the computability sense, like universal Turing machines).

Wait a minute, isn't it also the case that according to the Weierstrass approximation theorem any continuous function on a closed interval can be approximated by a polynomial function? And isn't that kind of pointless for practical applications because we also need to avoid overfitting? To clarify, I'm not trying to make a snippy remark, I just happened to have used polynomial curve fitting before and looked up the W…

[deleted]

Re: A visual proof that neural nets can approximate any function

#58

Any deeplearning expert here. Why Neural network can't compute a linear function Celsius to Fahrenheit 100% accurately. Is it data or is it something can be optimised. ``` celsius_q = np.array([-40, -10, 0, 8, 15, 22, 38], dtype=float) fahrenheit_a = np.array([-40, 14, 32, 46, 59, 72, 100], dtype=float) for i,c in enumerate(celsius_q): print("{} degrees Celsius = {} degrees Fahrenheit".format(c, fahrenheit_a[i])) l0…

Set your weights manually, and you'll see that the network can easily compute any linear function.
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