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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _create_optimizer_node(self):
 """Create the optimizer node of the graph."""

        self.lr_var = tf.Variable(0.0, trainable=False)
        tvars = tf.trainable_variables()
        grads, _ = tf.clip_by_global_norm(tf.gradients(self.cost, tvars),
                                          self.max_grad_norm)
        optimizer = tf.train.GradientDescentOptimizer(self.lr_var)
        self._train_op = optimizer.apply_gradients(zip(grads, tvars))