python - How to deactivate a dropout layer called with training=True in a Keras model?

Question

I wish to view the final output of training a tf.keras model. In this case it would be an array of predictions from the softmax function, e.g. [0,0,0,1,0,1].

Other threads on here have suggested using model.predict(training_data), but this won't work for my situation since I am using dropout at training and validation, so neurons are randomly dropped and predicting again with the same data will give a different result.

def get_model():
    inputs = tf.keras.layers.Input(shape=(input_dims,))
    x = tf.keras.layers.Dropout(rate=dropout_rate)(inputs, training=True)
    x = tf.keras.layers.Dense(units=29, activation='relu')(x)
    x = tf.keras.layers.Dropout(rate=dropout_rate)(x, training=True)  
    x = tf.keras.layers.Dense(units=15, activation='relu')(x)
    outputs = tf.keras.layers.Dense(2, activation='softmax')(x)
    model = tf.keras.Model(inputs=inputs, outputs=outputs)
    model.compile(optimizer='adam',
                  loss='sparse_categorical_crossentropy',      
                  metrics=['sparse_categorical_accuracy'])
    return model

myModel = get_model()
myModel.summary()
myModel.fit(X_train, y_train,
           batch_size = batch_size,
           epochs= epochs,
           verbose = 1,
           validation_data = (X_val, y_val))

In tensorflow, you can grab the output of a model after training quite easily. Here is an example from a Github repo:

input = tf.placeholder(tf.float32, shape=[None, INPUT_DIMS])
labels = tf.placeholder(tf.float32, shape=[None])

hidden = tf.nn.tanh(make_nn_layer(normalized, NUM_HIDDEN))
logits = make_nn_layer(hidden, NUM_CLASSES)
outputs = tf.argmax(logits, 1)

int_labels = tf.to_int64(labels)
cross_entropy = tf.nn.sparse_softmax_cross_entropy_with_logits(logits, int_labels, name='xentropy')
train_step = tf.train.AdamOptimizer().minimize(cross_entropy)

correct_prediction = tf.equal(outputs, int_labels)
accuracy = tf.reduce_mean(tf.cast(correct_prediction, tf.float32))

with tf.Session() as sess:
    sess.run(tf.initialize_all_variables())

    validation_dict = {
        input: validation_data[:,0:7],
        labels: validation_data[:,7],}

    for i in range(NUM_BATCHES):
        batch = training_data[numpy.random.choice(training_size, BATCH_SIZE, False),:]
        train_step.run({input: batch[:,0:7], labels: batch[:,7]})

        if i % 100 == 0 or i == NUM_BATCHES - 1:
            print('Accuracy %.2f%% at step %d' % (accuracy.eval(validation_dict) * 100, i))

    output_data = outputs.eval({input: data_vector[:,0:7]})

The only output I can get from the trained model appears to be a history object. There is also a myModel.output object, but it is a tensor that I can't evaluate without putting data into it. Any ideas?

Answer 1

As far as I know, you can't turn off the dropout after passing training=True when calling the layers (unless you transfer the weights to a new model with the same architecture). However, instead you can build and train your model in normal case (i.e. without using training argument in the calls) and then selectively turn on and off the dropout layer in test phase by defining a backend function (i.e. keras.backend.function()) and setting the learning phase (i.e. keras.backend.learning_phase()):

# build your model normally (i.e. without using `training=True` argument)

# train your model...

from keras import backend as K

func = K.function(model.inputs + [K.learning_phase()], model.outputs)

# run the model with dropout layers being active, i.e. learning_phase == 1
preds = func(list_of_input_arrays + [1])

# run the model with dropout layers being inactive, i.e. learning_phase == 0
preds = func(list_of_input_arrays + [0])

Update: As I suggested above, another approach is to define a new model with the same architecture but without setting training=True, and then transfer the weights from the trained model to this new model. To achieve this, I just add a training argument to your get_model() function:

def get_model(training=None):
    inputs = tf.keras.layers.Input(shape=(input_dims,))
    x = tf.keras.layers.Dropout(rate=dropout_rate)(inputs, training=training)
    x = tf.keras.layers.Dense(units=29, activation='relu')(x)
    x = tf.keras.layers.Dropout(rate=dropout_rate)(x, training=training)  
    x = tf.keras.layers.Dense(units=15, activation='relu')(x)
    outputs = tf.keras.layers.Dense(2, activation='softmax')(x)
    model = tf.keras.Model(inputs=inputs, outputs=outputs)
    model.compile(optimizer='adam',
                  loss='sparse_categorical_crossentropy',      
                  metrics=['sparse_categorical_accuracy'])
    return model

# build a model with dropout layers active in both training and test phases
myModel = get_model(training=True)
# train the model
myModel.fit(...)

# build a clone of the model with dropouts deactivated in test phase
myTestModel = get_model()  # note: the `training` is `None` by default
# transfer the weights from the trained model to this model
myTestModel.set_weights(myModel.get_weights())
# use the new model in test phase; the dropouts would not be active
myTestModel.predict(...)