code: def apply_mv_norm(features):
      # If there is less than 2 spectrograms, the variance cannot be computed (is NaN)
      # and normalization is not possible, so return the item as it is
      if features.size(0) < 2:
          return features
      mean, invstddev = calc_mean_invstddev(features)
      res = (features - mean) * invstddev
      return res
  
imports: import torch
label_desc: Use image node_id 2 for calling a global function with example usage: apply_mv_norm(features) and returns: res, features