code: def potential_fn(q):
      return 0.5 * q["x"] ** 2
  
imports: import logging
  from collections import namedtuple
  import pytest
  import torch
  from pyro.ops.integrator import velocity_verlet
  from tests.common import assert_equal
label_desc: Use image node_id 3 for calling the HarmonicOscillator obj's underlying member method code with example usage: obj.potential_fn(q) and returns: unknown