code: def forward(self, t, state):
      pos, vel, log_radius = state
      dpos = vel
      dvel = -self.gravity
      return dpos, dvel, torch.zeros_like(log_radius)
  
file_path: torchdiffeq/examples/bouncing_ball.py
imports: import argparse
  import matplotlib.pyplot
  import torch
  import torch.nn
  from torchdiffeq import odeint, odeint_adjoint
  from torchdiffeq import odeint_event
label_desc: Use image node_id 2 for calling the BouncingBallExample obj's underlying member method code with example usage: obj.forward(t, state) and returns: dpos,  dvel,  torch