Usage of loss functions
A loss function (or objective function, or optimization score function) is one of the two parameters required to compile a model:
model.compile(loss='mean_squared_error', optimizer='sgd')
from keras import losses
model.compile(loss=losses.mean_squared_error, optimizer='sgd')
You can either pass the name of an existing loss function, or pass a TensorFlow/Theano symbolic function that returns a scalar for each data-point and takes the following two arguments:
- y_true: True labels. TensorFlow/Theano tensor.
- y_pred: Predictions. TensorFlow/Theano tensor of the same shape as y_true.
The actual optimized objective is the mean of the output array across all datapoints.
For a few examples of such functions, check out the losses source.
Available loss functions
mean_squared_error
mean_squared_error(y_true, y_pred)
mean_absolute_error
mean_absolute_error(y_true, y_pred)
mean_absolute_percentage_error
mean_absolute_percentage_error(y_true, y_pred)
mean_squared_logarithmic_error
mean_squared_logarithmic_error(y_true, y_pred)
squared_hinge
squared_hinge(y_true, y_pred)
hinge
hinge(y_true, y_pred)
categorical_hinge
categorical_hinge(y_true, y_pred)
logcosh
logcosh(y_true, y_pred)
categorical_crossentropy
categorical_crossentropy(y_true, y_pred)
sparse_categorical_crossentropy
sparse_categorical_crossentropy(y_true, y_pred)
binary_crossentropy
binary_crossentropy(y_true, y_pred)
kullback_leibler_divergence
kullback_leibler_divergence(y_true, y_pred)
poisson
poisson(y_true, y_pred)
cosine_proximity
cosine_proximity(y_true, y_pred)
Note: when using the categorical_crossentropy
loss, your targets should be in categorical format (e.g. if you have 10 classes, the target for each sample should be a 10-dimensional vector that is all-zeros expect for a 1 at the index corresponding to the class of the sample). In order to convert integer targets into categorical targets, you can use the Keras utility to_categorical
:
from keras.utils.np_utils import to_categorical
categorical_labels = to_categorical(int_labels, num_classes=None)