## 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:
“`python
model.compile(loss=’mean_squared_error’, optimizer=’sgd’)
“`
“`python
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](https://github.com/keras-team/keras/blob/master/keras/losses.py).
## Available loss functions
{{autogenerated}}
—-
**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 except 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`:
“`python
from keras.utils.np_utils import to_categorical
categorical_labels = to_categorical(int_labels, num_classes=None)
“`