Tensorflow training - print multiple losses for one output

Question

I would like to print all the different losses I have for one output separately. At the moment it looks like:

1/1 [==============================] - 1s 1s/sample - loss: 4.2632

The goal is to have a history like:

1/1 [==============================] - 1s 1s/sample - loss1: 2.1, loss2: 2.1632

I have one output layer out1 and two loss functions loss1 and loss2.

def loss1(y_true, y_pred):
    ...
    return ...

def loss2(y_true, y_pred):
    ...
    return ...

When I do

model.compile(...)

I can either choose to have a single loss function,

model.compile(loss=lambda x: loss1(x) + loss2(x))

or defining a loss for each output in a dictionary

model.compile(loss={'out1': loss1(x), 'out2': loss2(x)})

Since I have only one output, this isn't an option for me. Does anyone know how to print the losses separately when having only one output?

Answer 1

Just use the metrics argument:

model.compile(optimizer='adam', loss='mae', metrics=['mse'])

You will still need to choose one loss to minimize.

Answer 2

One workaround is to artificially create the same two outputs, and then combine them with weights equal 1. For the sake of concreteness, I wrote the example:

from tensorflow.keras import Model
from tensorflow.keras.layers import Input, Dense, Lambda
from tensorflow.keras.losses import mse, mae
import numpy as np

if __name__ == '__main__':
    train_x = np.random.rand(10000, 200)
    train_y = np.random.rand(10000, 1)

    x_input = Input(shape=(200))
    x = Dense(64)(x_input)
    x = Dense(64)(x)
    x = Dense(1)(x)

    x1 = Lambda(lambda x: x, name='out1')(x)
    x2 = Lambda(lambda x: x, name='out2')(x)

    model = Model(inputs=x_input, outputs=[x1, x2])

    model.compile(optimizer='adam', loss={'out1': mse, 'out2': mae}, loss_weights={'out1': 1, 'out2': 1})

    model.fit(train_x, train_y, epochs=10)