code: def test_grid_constructor(self):
      def f(t, x):
          return x
  
      for adjoint in (False, True):
          with self.subTest(adjoint=adjoint):
              x0 = torch.tensor(1.0, requires_grad=True)
              t = torch.tensor([0.0, 1.0])
  
              first = True
  
              def grid_constructor(f, y0, t):
                  nonlocal first
                  self.assertEqual(t.shape, (2,))
                  if first:
                      first = False
                      self.assertEqual(t[0], 0.0)
                      self.assertEqual(t[1], 1.0)
                      return torch.linspace(0, 1, 11)
                  else:
                      # adjoint pass
                      self.assertEqual(t[0], 1.0)
                      self.assertEqual(t[1], 0.0)
                      return torch.linspace(1, 0, 11)
  
              odeint = (
                  torchdiffeq.odeint_adjoint
                  if adjoint
                  else torchdiffeq.odeint
              )
              kwargs = {"adjoint_params": ()} if adjoint else {}
              xs = odeint(
                  f,
                  x0,
                  t,
                  method="euler",
                  options=dict(grid_constructor=grid_constructor),
                  **kwargs,
              )
              x1 = xs[1]
  
              # 'true' wrt the use of the Euler scheme
              true_x1 = x0 * 1.1**10
              self.assertLess((x1 - true_x1).abs().max(), 1e-6)
              if adjoint:
                  x1.backward()
                  # 'true' wrt the use of the Euler scheme
                  true_x0_grad = 1.1**10
                  self.assertLess(
                      (x0.grad - true_x0_grad).abs().max(), 1e-6
                  )
  
imports: from functools import partial
  import unittest
  import warnings
  import torch
  import torchdiffeq
  from problems import construct_problem, PROBLEMS, DTYPES, DEVICES, METHODS, ADAPTIVE_METHODS, FIXED_METHODS, SCIPY_METHODS
label_desc: Use image node_id 1 for calling the TestGridConstructor obj's underlying member method code with example usage: obj.test_grid_constructor() and returns: x, torch, torch