text: # Copyright 2017 reinforce.io. All Rights Reserved.
  #
  # Licensed under the Apache License, Version 2.0 (the "License");
  # you may not use this file except in compliance with the License.
  # You may obtain a copy of the License at
  #
  #     http://www.apache.org/licenses/LICENSE-2.0
  #
  # Unless required by applicable law or agreed to in writing, software
  # distributed under the License is distributed on an "AS IS" BASIS,
  # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  # See the License for the specific language governing permissions and
  # limitations under the License.
  # ==============================================================================
  
  """
  Standardize data (z-transformation)
  """
  
  from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  
  import numpy as np
  
  from tensorforce import util
  from tensorforce.core.preprocessing import Preprocessor
  
  
  class Normalize(Preprocessor):
      """
      Normalize state. Subtract mean and divide by standard deviation.
      """
  
      def process(self, state):
          state = state.astype(np.float32)
          return (state - state.mean()) / (state.std() + util.epsilon)
  