docstr: Test for the case where all terms (quadratic, linear, shift) are null.
docstr_tok: ["Test","for","the","case","where","all","terms","(","quadratic",",","linear",",","shift",")","are","null","."]
code: def testNoTimeDependence(self):
      """Test for the case where all terms (quadratic, linear, shift) are null."""
      grid = grids.uniform_grid(
          minimums=[-10, -20],
          maximums=[10, 20],
          sizes=[201, 301],
          dtype=tf.float32,
      )
      ys = self.evaluate(grid[0])
      xs = self.evaluate(grid[1])
  
      time_step = 0.1
      final_t = 1
      variance = 1
  
      final_cond = np.outer(
          _gaussian(ys, variance), _gaussian(xs, variance)
      )
      final_values = tf.expand_dims(
          tf.constant(final_cond, dtype=tf.float32), axis=0
      )
      bound_cond = [
          (_zero_boundary, _zero_boundary),
          (_zero_boundary, _zero_boundary),
      ]
      step_fn = douglas_adi_step(theta=0.5)
      result = fd_solvers.solve_backward(
          start_time=final_t,
          end_time=0,
          coord_grid=grid,
          values_grid=final_values,
          time_step=time_step,
          one_step_fn=step_fn,
          boundary_conditions=bound_cond,
          dtype=grid[0].dtype,
      )
      expected = final_cond  # No time dependence.
      self._assertClose(expected, result)
  
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 11 for calling the MultidimParabolicEquationStepperTest obj's underlying member method code with example usage: obj.testNoTimeDependence() without return types