code: def logSE(x1, x2=-1):
      
      e = get_valid_error(x1, x2)
      return 10*np.log10(e**2)
docs: 10 * log10(e**2)    
      This function accepts two series of data or directly
      one series with error.
  
      **Args:**
  
      * `x1` - first data series or error (1d array)
  
      **Kwargs:**
  
      * `x2` - second series (1d array) if first series was not error directly,\\
          then this should be the second series
  
      **Returns:**
  
      * `e` - logSE of error (1d array) obtained directly from `x1`, \\
          or as a difference of `x1` and `x2`. The values are in dB!