Move optimizer closer to usage

tutorials/image/cifar10_estimator/cifar10_main.py

@@ -155,9 +155,6 @@ def get_model_fn(num_gpus, variable_strategy, num_workers):
                                                   boundaries, staged_lr)
 
       loss = tf.reduce_mean(tower_losses, name='loss')
-      optimizer = tf.train.MomentumOptimizer(
-          learning_rate=learning_rate, momentum=momentum)
-
 
       examples_sec_hook = cifar10_utils.ExamplesPerSecondHook(
           params.train_batch_size, every_n_steps=10)
@@ -168,6 +165,10 @@ def get_model_fn(num_gpus, variable_strategy, num_workers):
           tensors=tensors_to_log, every_n_iter=100)
 
       train_hooks = [logging_hook, examples_sec_hook]
+
+      optimizer = tf.train.MomentumOptimizer(
+          learning_rate=learning_rate, momentum=momentum)
+
       if params.sync:
         optimizer = tf.train.SyncReplicasOptimizer(
             optimizer, replicas_to_aggregate=num_workers)