code: def par_final_stepgrp(i):
      
  
      par_y0bstep(i)
      par_y1step(i)
      par_u0step(i)
      par_u1step(i)
docs: The parallel step grouping of the final iteration in solve. A
      cyclic permutation of the steps is done to require only one merge
      per iteration, requiring unique initial and final step groups.
  
      Parameters
      ----------
      i : int
        Index of grouping to update