code: def delta(a, b, ref, fraction=0.9):
      length = a.shape[-1]
      compare_length = int(length * fraction)
      offset = (length - compare_length) // 2
      a = a[..., offset : offset + length]
      b = b[..., offset : offset + length]
      return 100 * th.abs(a - b).mean() / ref.std()
  
imports: import random
  import unittest
  import torch
  from julius.core import pure_tone
  from julius import filters
label_desc: Use image node_id 1 for calling a global function with example usage: delta(a, b, ref, fraction) and returns: unknown