code: def plot_histograms(self, freq=None, title=None,
                          figsize=(10, 10), **kwargs):
          
          if title is None:
              title = self._get_default_plot_title(
                  freq, 'Return Histogram Matrix')
  
          plt.figure()
          ser = self._get_series(freq).to_returns().dropna()
          ser.hist(figsize=figsize, **kwargs)
          return plt.suptitle(title)
docs: Wrapper around pandas' hist.
  
          Args:
              * freq (str): Data frequency used for display purposes.
                  Refer to pandas docs for valid freq strings.
              * figsize ((x,y)): figure size
              * title (str): Title if default not appropriate
              * kwargs: passed to pandas' hist method