class_docstr: Task for policy evaluation.
class_docstr_tok: ["Task","for","policy","evaluation","."]
code: def entropy_metric(self):
      def Entropy(policy_inputs, actions, advantages, mask):
          del actions, advantages, mask
          return jnp.mean(self._policy_dist.entropy(policy_inputs))
  
      return tl.Fn("Entropy", Entropy)
  
file_path: trax/trax/rl/policy_tasks.py
imports: import numpy
  from trax import layers
  from trax.fastmath import numpy
  from trax.rl import distributions
  from trax.supervised import training
label_desc: Use image node_id 3 for calling the PolicyEvalTask obj's underlying member method code with example usage: obj.entropy_metric() and returns: tl, jnp