code: def forward(self, t, state):
      # IMPORTANT: event computation must use variables from the state.
      pos, _, radius = state
      return pos - radius.reshape_as(pos) ** 2
  
imports: import argparse
  import os
  import math
  import matplotlib.pyplot
  import torch
  import torch.nn
  from torchdiffeq import odeint, odeint_event
  from bouncing_ball import BouncingBallExample
label_desc: Use image node_id 3 for calling the EventFn obj's underlying member method code with example usage: obj.forward(t, state) and returns: unknown