code: def optimizer(self):
      lr = tf.get_variable(
          "learning_rate", initializer=1e-4, trainable=False
      )
      return tf.train.GradientDescentOptimizer(lr)
  
imports: import argparse
  import numpy
  import tensorflow
  import tensorflow.contrib.slim
  from tensorpack import *
  from tensorpack.tfutils.summary import add_moving_summary
  from tensorpack.utils.gpu import change_gpu
  from embedding_data import MnistPairs, MnistTriplets, get_test_data
label_desc: Use image node_id 2 for calling the EmbeddingModel obj's underlying member method code with example usage: obj.optimizer() and returns: tf