Train neural network with sine function

问题

I want to train a neural network with the sine() function.

Currently I use this code and the (cerebrum gem):

require 'cerebrum'

input = Array.new
300.times do |i|
  inputH = Hash.new
  inputH[:input]=[i]
  sinus = Math::sin(i)
  inputH[:output] = [sinus]
  input.push(inputH)

end

network = Cerebrum.new

network.train(input, {
  error_threshold: 0.00005,
  iterations:      40000,
  log:             true,
  log_period:      1000,
  learning_rate:   0.3
})


res = Array.new
300.times do |i|
  result = network.run([i])
  res.push(result[0])
end

puts "#{res}"

But it does not work, if I run the trained network I get some weird output values (instead of getting a part of the sine curve).

So, what I am doing wrong?

回答1:

Cerebrum is a very basic and slow NN implementation. There are better options in Ruby, such as ruby-fann gem.

Most likely your problem is the network is too simple. You have not specified any hidden layers - it looks like the code assigns a default hidden layer with 3 neurons in it for your case.

Try something like:

network = Cerebrum.new({
  learning_rate:  0.01,
  momentum:       0.9,
  hidden_layers:  [100]
})

and expect it to take forever to train, plus still not be very good.

Also, your choice of 300 outputs is too broad - to the network it will look mostly like noise and it won't interpolate well between points. A neural network does not somehow figure out "oh, that must be a sine wave" and match to it. Instead it interpolates between the points - the clever bit happens when it does so in multiple dimensions at once, perhaps finding structure that you could not spot so easily with a manual inspection. To give it a reasonable chance of learning something, I suggest you give it much denser points e.g. where you currently have sinus = Math::sin(i) instead use:

sinus = Math::sin(i.to_f/10)

That's still almost 5 iterations through the sine wave. Which should hopefully be enough to prove that the network can learn an arbitrary function.

来源：https://stackoverflow.com/questions/37756937/train-neural-network-with-sine-function