code: def _reference_2d_pde_solution(xs, ys, t, num_terms=5):
      return _dir_prod(
          _reference_pde_solution(ys, t, num_terms),
          _reference_pde_solution(xs, t, num_terms),
      )
  
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 5 for calling a global function with example usage: _reference_2d_pde_solution(xs, ys, t, num_terms) and returns: _dir_prod