code: def delta(feat, window):
      assert window > 0
      delta_feat = np.zeros_like(feat)
      for i in range(1, window + 1):
          delta_feat[:-i] += i * feat[i:]
          delta_feat[i:] += -i * feat[:-i]
          delta_feat[-i:] += i * feat[-1]
          delta_feat[:i] += -i * feat[0]
      delta_feat /= 2 * sum(i**2 for i in range(1, window + 1))
      return delta_feat
  
imports: import numpy
label_desc: Use image node_id 1 for calling a global function with example usage: delta(feat, window) and returns: delta_feat