class_docstr: Actor-Critic Policy Gradient.
  
  See https://arxiv.org/pdf/1602.01783.pdf for a description of algorithm.
docstr: Save model to file.
docstr_tok: ["Save","model","to","file","."]
code: def save(self, filename):
      """Save model to file."""
      self._best_model.save(filename)
  
imports: import cntk
  import numpy
  import ast
  from .agent import AgentBaseClass
  from .shared.cntk_utils import negative_of_entropy_with_softmax
  from .shared.models import Models
  from .shared.policy_gradient_parameters import PolicyGradientParameters
label_desc: Use image node_id 9 for calling the ActorCritic obj's underlying member method code with example usage: obj.save(filename) without return types