code: def save_spectre_plot(self, filename="spectre.pdf", img_format="pdf",
                            sigma=0.05, step=0.01):
          
          d, plt = self.get_spectre_plot(sigma, step)
          plt.savefig(filename, format=img_format)
docs: Save matplotlib plot of the spectre to a file.
  
          Args:
              filename: Filename to write to.
              img_format: Image format to use. Defaults to EPS.
              sigma: Full width at half maximum in eV for normal functions.
              step: bin interval in eV