code: def A4():
      diffeq = lambda t, y: y / 4 * (1 - y / 20)
      init = lambda: (torch.tensor(0.0), torch.tensor(1.0))
      solution = lambda t: 20 / (1 + 19 * torch.exp(-t / 4))
      return diffeq, init, solution
  
imports: import math
  import torch
label_desc: Use image node_id 4 for calling a global function with example usage: A4() and returns: diffeq,  init,  solution