class_docstr: Morris test function.
  
  20-dimensional function (usually evaluated on `[0, 1]^20`):
  
      f(x) = sum_{i=1}\^20 beta_i w_i + sum_{i<j}\^20 beta_ij w_i w_j
      + sum_{i<j<l}\^20 beta_ijl w_i w_j w_l + 5w_1 w_2 w_3 w_4
  
  Proposed to test sensitivity analysis methods
code: def _optimal_value(self) -> float:
      raise NotImplementedError
  
imports: import math
  from typing import List, Optional, Tuple
  import torch
  from botorch.test_functions.synthetic import SyntheticTestFunction
  from torch import Tensor
label_desc: Use image node_id 2 for calling the Morris obj's underlying member method code with example usage: obj._optimal_value() without return types