code: def optimizer(self):
      lr = tf.train.exponential_decay(
          learning_rate=1e-3,
          global_step=get_global_step_var(),
          decay_steps=4721 * 60,
          decay_rate=0.2,
          staircase=True,
          name="learning_rate",
      )
      tf.summary.scalar("lr", lr)
      return tf.train.AdamOptimizer(lr)
  
file_path: tensorpack/examples/basics/svhn-digit-convnet.py
imports: import argparse
  import os
  from tensorpack import tfv1
  from tensorpack import *
  from tensorpack.dataflow import dataset
  from tensorpack.tfutils.summary import *
label_desc: Use image node_id 3 for calling the Model obj's underlying member method code with example usage: obj.optimizer() and returns: tf