I am experimenting with Neural networks for regression tasks. I know some theory, and how to choose the activation function for the output layer. What is not clear to me is: how to choose activation for hidden layers?
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2 Answers
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With respect to choosing hidden layer activations, I don't think that there's anything about a regression task which is different from other neural network tasks: you should use nonlinear activations so that the model is nonlinear (otherwise, you're just doing a very slow, expensive linear regression), and you should use activations that are easy to train (ReLU or similar).
Recent research has found that ReLU and similar activations (ELU, Leaky ReLU, etc.) work very well because they allow researchers to build deep networks which do not suffer from vanishing or exploding gradient for positive inputs. See:
- How does rectilinear activation function solve the vanishing gradient problem in neural networks?
- What are the advantages of ReLU over sigmoid function in deep neural networks?
- Why can't a single ReLU learn a ReLU?
On the left, ReLU has derivative 0 and this can lead to the "dead ReLU" phenomenon. So I prefer using ELU or LeakyReLU units, which can be more robust to that problem.
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Hyperbolic tangent and sigmoid transfer functions are usually implemented in the hiddens layers of the various neural network fitting tools in Matlab,R,ecc.. Their use is similar and you can try them very simply.They are both differentiable and continous.ReLU and similar are usually implemented in the convolutional neural networks but I don't think it is the first choice for your problem.