code: def testMultiMeshBackward(self):
      self.skipForDeviceType(
          ["CPU"],
          "Skipping test as only CPU mesh is available for multi-meshtest.",
      )
  
      replicated_layout_on_tpu = Layout.replicated(
          self.second_mesh, rank=1
      )
      host_layout = Layout.replicated(
          self.second_mesh.host_mesh(), rank=1
      )
  
      source_layout = host_layout
      target_layout = replicated_layout_on_tpu
  
      @polymorphic_function.function
      def func(x):
          with backprop.GradientTape() as tape:
              tape.watch(x)
              x = x * 4.0
              t = api.copy_to_mesh(x, target_layout)
              sqrt = math_ops.sqrt(t)
              sqrt_grad = tape.gradient(sqrt, x)
              return sqrt_grad
  
      @polymorphic_function.function
      def second(x):
          with backprop.GradientTape() as tape:
              tape.watch(x)
              sqrt_grad = func(x)
              sqrt_grad_grad = tape.gradient(sqrt_grad, x)
              return sqrt_grad_grad
  
      numpy_a = constant_op.constant(
          [1, 4, 16, 64], dtype=dtypes.float32
      )
      a = api.copy_to_mesh(numpy_a, source_layout)
  
      with ops.device_v2(api.device_name()):
          a_grad = func(a)
  
      self.assertDTensorEqual(
          0.5 * 0.5 * (1 / numpy_a) ** 0.5, host_layout, a_grad
      )
      with ops.device_v2(api.device_name()):
          a_grad_grad = second(a)
      self.assertDTensorEqual(
          -0.5 * 0.5 * 0.5 * (1 / numpy_a) ** 1.5,
          host_layout,
          a_grad_grad,
      )
  
imports: from absl.testing import parameterized
  import numpy
  from tensorflow.dtensor.python import accelerator_util
  from tensorflow.dtensor.python import api
  from tensorflow.dtensor.python import config
  from tensorflow.dtensor.python import d_variable
  from tensorflow.dtensor.python import layout
  from tensorflow.dtensor.python.tests import test_util
  from tensorflow.python.eager import backprop
  from tensorflow.python.eager import context
  from tensorflow.python.eager.polymorphic_function import polymorphic_function
  from tensorflow.python.framework import constant_op
  from tensorflow.python.framework import dtypes
  from tensorflow.python.framework import errors_impl
  from tensorflow.python.framework import ops
  from tensorflow.python.ops import array_ops
  from tensorflow.python.ops import gen_math_ops
  from tensorflow.python.ops import math_ops
  from tensorflow.python.platform import test
label_desc: Use image node_id 20 for calling the MultiMeshTest obj's underlying member method code with example usage: obj.testMultiMeshBackward() and returns: sqrt_grad, sqrt_grad_grad