How is the hidden layer size determined for MLPRegressor in SciKitLearn?

Question

Lets say I\'m creating a neural net using the following code:

from sklearn.neural_network import MLPRegressor

model = MLPRegressor(
  hidden_layer_sizes=(100,),         


        

Answer 1

From the docs:

hidden_layer_sizes : tuple, length = n_layers - 2, default (100,)

The ith element represents the number of neurons in the ith hidden layer.

It is length = n_layers - 2, because the number of your hidden layers is the total number of layers n_layers minus 1 for your input layer, minus 1 for your output layer.

In your (default) case of (100,), it means one hidden layer of 100 units (neurons).

For 3 hidden layers of, say, 100, 50, and 25 units respectively, it would be

hidden_layer_sizes = (100, 50, 25)

See the example in the docs (it is for MLPClassifier, but the logic is identical).