code: def plot_neff(self, ax, xt_labelsize, titlesize, markersize):
          
          for plotter in self.plotters.values():
              for y, ess, color in plotter.ess():
                  if ess is not None:
                      ax.plot(
                          ess,
                          y,
                          "o",
                          color=color,
                          clip_on=False,
                          markersize=markersize,
                          markeredgecolor="k",
                      )
          ax.set_xlim(left=0)
          ax.set_title("ess", fontsize=titlesize, wrap=True)
          ax.tick_params(labelsize=xt_labelsize)
          return ax
docs: Draw effective n for each plotter.