code: def loss(self, theta):
      net = self.net
      net.variables.set_flat(theta)
      return net.loss(self.xs, self.ys)
  
file_path: ray/doc/source/ray-core/examples/lbfgs/driver.py
imports: import os
  import numpy
  import scipy.optimize
  import tensorflow
  from tensorflow.examples.tutorials.mnist import input_data
  import ray
  import ray.experimental.tf_utils
label_desc: Use image node_id 2 for calling the NetActor obj's underlying member method code with example usage: obj.loss(theta) and returns: net