How to restrict output of a neural net to a specific range?

Question

I'm using Keras for a regression task and want to restrict my output to a range (say between 1 and 10)

Is there a way to ensure this?

Answer 1

Write a custom activation function like this

# a simple custom activation
from keras import backend as BK
def mapping_to_target_range( x, target_min=1, target_max=10 ) :
    x02 = BK.tanh(x) + 1 # x in range(0,2)
    scale = ( target_max-target_min )/2.
    return  x02 * scale + target_min

# create a simple model
from keras.layers import Input, Dense
from keras.models import Model
x = Input(shape=(1000,))
y = Dense(4, activation=mapping_to_target_range )(x)
model = Model(inputs=x, outputs=y)

# testing
import numpy as np 
a = np.random.randn(10,1000)
b = model.predict(a)
print b.min(), b.max()

And you are expected to see the min and max values of b are very close to 1 and 10, respectively.