code: def check_backward(self, diag_data, non_diag_data, gpu):
      diag = torch.tensor(diag_data, requires_grad=True)
      non_diag = torch.tensor(non_diag_data, requires_grad=True)
      if gpu >= 0:
          diag = diag.to(torch.device("cuda", gpu))
          non_diag = non_diag.to(torch.device("cuda", gpu))
      torch.autograd.gradcheck(
          lower_triangular_matrix,
          (diag, non_diag),
          eps=1e-02,
          rtol=1e-2,
      )
  
file_path: pfrl/tests/functions_tests/test_lower_triangular_matrix.py
imports: import numpy
  import pytest
  import torch
  from pfrl.functions.lower_triangular_matrix import lower_triangular_matrix
label_desc: Use image node_id 5 for calling the TestLowerTriangularMatrix obj's underlying member method code with example usage: obj.check_backward(diag_data, non_diag_data, gpu) without return types