Keras: change learning rate

You can change the learning rate as follows:

from keras import backend as K
K.set_value(model.optimizer.learning_rate, 0.001)

Included into your complete example it looks as follows:

from keras.models import Sequential
from keras.layers import Dense
from keras import backend as K
import keras
import numpy as np

model = Sequential()

model.add(Dense(1, input_shape=(10,)))

optimizer = keras.optimizers.Adam(lr=0.01)
model.compile(loss="mse", optimizer=optimizer)

print("Learning rate before first fit:", model.optimizer.learning_rate.numpy())

model.fit(np.random.randn(50,10), np.random.randn(50), epochs=50, verbose=0)

# Change learning rate to 0.001 and train for 50 more epochs
K.set_value(model.optimizer.learning_rate, 0.001)
print("Learning rate before second fit:", model.optimizer.learning_rate.numpy())

model.fit(np.random.randn(50,10), 
          np.random.randn(50), 
          initial_epoch=50, 
          epochs=50,
          verbose=0)

I’ve just tested this with keras 2.3.1. Not sure why the approach didn’t seem to work for you.