def METHOD_NAME(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)