docs: def post_process_data(self, voltage=None, incremental_capacity=None,
                            voltage_step=None):
          """perform post-processing (smoothing, normalisation, interpolation) of
          the data"""
  
          logging.debug("post-processing data")
  
          if voltage is None:
              voltage = self.voltage_processed
              incremental_capacity = self.incremental_capacity
              voltage_step = self.voltage_inverted_step
  
          if self.post_smoothing:
              logging.debug(" - post smoothing (gaussian)")
              logging.debug(f"    * using voltage fwhm: {self.voltage_fwhm}")
              points_fwhm = int(self.voltage_fwhm / voltage_step)
  
              sigma = np.amax([1, points_fwhm / 2])
  
              self.incremental_capacity = gaussian_filter1d(
                  incremental_capacity, sigma=sigma, order=self.gaussian_order,
                  mode=self.gaussian_mode,
                  cval=self.gaussian_cval,
                  truncate=self.gaussian_truncate
              )
  
          if self.normalize:
              logging.debug(" - normalizing")
              area = simps(incremental_capacity, voltage)
              self.incremental_capacity = incremental_capacity * self.normalizing_factor / abs(area)
  
          fixed_range = False
          if isinstance(self.fixed_voltage_range, np.ndarray):
              fixed_range = True
          else:
              if self.fixed_voltage_range:
                  fixed_range = True
          if fixed_range:
              logging.debug(" - using fixed voltage range (interpolating)")
              v1, v2, number_of_points = self.fixed_voltage_range
              v = np.linspace(v1, v2, number_of_points)
              f = interp1d(x=self.voltage_processed, y=self.incremental_capacity,
                           kind=self.interpolation_method, bounds_error=False,
                           fill_value=np.NaN)
  
              self.incremental_capacity = f(v)
              self.voltage_processed = v