code: def three_var_approx(three_var_model, three_var_groups):
      approx = opvi.Approximation(
          three_var_groups, model=three_var_model
      )
      return approx
  
imports: import functools
  import numpy
  import pytensor.tensor
  import pytest
  import pymc
  from pymc.variational import opvi
  from pymc.variational.approximations import Empirical, EmpiricalGroup, FullRank, FullRankGroup, MeanField, MeanFieldGroup
  from tests.helpers import not_raises
label_desc: Use image node_id 8 for calling a global function with example usage: three_var_approx(three_var_model, three_var_groups) and returns: approx