code: def _reference_2d_pde_initial_cond(xs, ys):
      """Initial conditions for the reference 2d diffusion equation."""
      return _dir_prod(
          _reference_pde_initial_cond(ys),
          _reference_pde_initial_cond(xs),
      )
  
imports: from absl.testing import parameterized
  import numpy
  import tensorflow.compat.v2
  import tf_quant_finance
  from tensorflow.python.framework import test_util
label_desc: Use image node_id 4 for calling a global function with example usage: _reference_2d_pde_initial_cond(xs, ys) and returns: _dir_prod