code: def backward(ctx, grad_scratch):
      return grad_scratch, grad_scratch[ctx.index], None
  
imports: import bisect
  import collections
  import torch
  from .event_handling import find_event
  from .interp import _interp_evaluate, _interp_fit
  from .misc import _compute_error_ratio, _select_initial_step, _optimal_step_size
  from .misc import Perturb
  from .solvers import AdaptiveStepsizeEventODESolver
label_desc: Use image node_id 2 for calling the _UncheckedAssign obj's underlying member method code with example usage: obj.backward(ctx, grad_scratch) and returns: grad_scratch,  grad_scratch,  None