<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _get_lr_tensor(self):
 """Get lr minimizing the surrogate. Returns: The lr_t. """

    lr = tf.squared_difference(1.0, tf.sqrt(self._mu)) / self._h_min
    return lr