code: def rk3_step_func(
      func, t0, dt, t1, y0, butcher_tableu=None, f0=None, perturb=False
  ):
      """butcher_tableu should be of the form
  
      [
          [0  , 0     , 0     ,   0],
          [c_2, a_{21}, 0     ,   0],
          [c_3, a_{31}, a_{32},   0],
          [0  , b_1   , b_2   , b_3],
      ]
  
      https://en.wikipedia.org/wiki/List_of_Runge-Kutta_methods
      """
      k1 = f0
      if k1 is None:
          k1 = func(
              t0, y0, perturb=Perturb.NEXT if perturb else Perturb.NONE
          )
  
      k2 = func(
          t0 + dt * butcher_tableu[1][0],
          y0 + dt * k1 * butcher_tableu[1][1],
      )
      k3 = func(
          t0 + dt * butcher_tableu[2][0],
          y0
          + dt
          * (k1 * butcher_tableu[2][1] + k2 * butcher_tableu[2][2]),
      )
      return dt * (
          k1 * butcher_tableu[3][1]
          + k2 * butcher_tableu[3][2]
          + k3 * butcher_tableu[3][3]
      )
  
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 4 for calling a global function with example usage: rk3_step_func(func, t0, dt, t1, y0, butcher_tableu, f0, perturb) and returns: unknown