old_contents: """====================================================
                      DESCRIPTION
  
  =======================================================
  """
  __author__ = 'ronny'
  
  import numpy as np
  
  def normalise_columns(x, mean, sd):
      return (np.array(x) - mean) / sd
  
  
  
new_contents: """====================================================
                      DESCRIPTION
  
  =======================================================
  """
  __author__ = 'ronny'
  
  import numpy as np
  
  def normalise_columns(x, mean, sd):
      return (np.array(x) - mean) / sd
  
  
  def un_normalise_columns(z, mean, sd):
      return z*sd + mean
  
subject: Add un_normalise_columns()