Keras之自定义损失(loss)函数用法说明

在keras中可以自定义损失函数，在自定义损失函数的过程中需要注意的一点是，损失函数的参数形式，这一点在keras中是固定的，须如下形式：

def my_loss(y_true, y_pred):
# y_true: true labels. tensorflow/theano tensor
# y_pred: predictions. tensorflow/theano tensor of the same shape as y_true
 .
 .
 .
 return scalar #返回一个标量值

然后在model.compile中指定即可，如：

model.compile(loss=my_loss, optimizer='sgd')

具体参考keras官方metrics的定义keras/metrics.py：

"""built-in metrics.
"""
from __future__ import absolute_import
from __future__ import division
from __future__ import print_function
 
import six
from . import backend as k
from .losses import mean_squared_error
from .losses import mean_absolute_error
from .losses import mean_absolute_percentage_error
from .losses import mean_squared_logarithmic_error
from .losses import hinge
from .losses import logcosh
from .losses import squared_hinge
from .losses import categorical_crossentropy
from .losses import sparse_categorical_crossentropy
from .losses import binary_crossentropy
from .losses import kullback_leibler_divergence
from .losses import poisson
from .losses import cosine_proximity
from .utils.generic_utils import deserialize_keras_object
from .utils.generic_utils import serialize_keras_object
 
def binary_accuracy(y_true, y_pred):
 return k.mean(k.equal(y_true, k.round(y_pred)), axis=-1)
 
 
def categorical_accuracy(y_true, y_pred):
 return k.cast(k.equal(k.argmax(y_true, axis=-1),
       k.argmax(y_pred, axis=-1)),
     k.floatx())
 
def sparse_categorical_accuracy(y_true, y_pred):
 # reshape in case it's in shape (num_samples, 1) instead of (num_samples,)
 if k.ndim(y_true) == k.ndim(y_pred):
  y_true = k.squeeze(y_true, -1)
 # convert dense predictions to labels
 y_pred_labels = k.argmax(y_pred, axis=-1)
 y_pred_labels = k.cast(y_pred_labels, k.floatx())
 return k.cast(k.equal(y_true, y_pred_labels), k.floatx())
 
def top_k_categorical_accuracy(y_true, y_pred, k=5):
 return k.mean(k.in_top_k(y_pred, k.argmax(y_true, axis=-1), k), axis=-1)
 
def sparse_top_k_categorical_accuracy(y_true, y_pred, k=5):
 # if the shape of y_true is (num_samples, 1), flatten to (num_samples,)
 return k.mean(k.in_top_k(y_pred, k.cast(k.flatten(y_true), 'int32'), k),
     axis=-1)
 
# aliases
 
mse = mse = mean_squared_error
mae = mae = mean_absolute_error
mape = mape = mean_absolute_percentage_error
msle = msle = mean_squared_logarithmic_error
cosine = cosine_proximity
 
def serialize(metric):
 return serialize_keras_object(metric)
 
def deserialize(config, custom_objects=none):
 return deserialize_keras_object(config,
         module_objects=globals(),
         custom_objects=custom_objects,
         printable_module_name='metric function')
 
def get(identifier):
 if isinstance(identifier, dict):
  config = {'class_name': str(identifier), 'config': {}}
  return deserialize(config)
 elif isinstance(identifier, six.string_types):
  return deserialize(str(identifier))
 elif callable(identifier):
  return identifier
 else:
  raise valueerror('could not interpret '
       'metric function identifier:', identifier)

以上这篇keras之自定义损失(loss)函数用法说明就是小编分享给大家的全部内容了，希望能给大家一个参考，也希望大家多多支持。