code: def test_forward_nu_5_over_2(self):
      a = torch.tensor([4, 2, 8], dtype=torch.float).view(3, 1)
      b = torch.tensor([0, 2], dtype=torch.float).view(2, 1)
      lengthscale = 2
  
      kernel = MaternKernel(nu=2.5).initialize(lengthscale=lengthscale)
      kernel.eval()
  
      dist = torch.tensor(
          [[4, 2], [2, 0], [8, 6]], dtype=torch.float
      ).mul_(math.sqrt(5) / lengthscale)
      actual = (dist**2 / 3 + dist + 1).mul(torch.exp(-dist))
      res = kernel(a, b).to_dense()
      self.assertLess(torch.norm(res - actual), 1e-3)
  
imports: import math
  import pickle
  import unittest
  import torch
  from gpytorch.kernels import MaternKernel
  from gpytorch.priors import NormalPrior
  from gpytorch.test.base_kernel_test_case import BaseKernelTestCase
label_desc: Use image node_id 5 for calling the TestMaternKernel obj's underlying member method code with example usage: obj.test_forward_nu_5_over_2() without return types