code: def plot_fracs(self, Q=None, ax=None, fignum=None):
          from ..plotting import Tango
          Tango.reset()
          col = Tango.nextMedium()
          if ax is None:
              fig = pylab.figure(fignum)
              ax = fig.add_subplot(111)
          if Q is None:
              Q = self.Q
          ticks = numpy.arange(Q)
          bar = ax.bar(ticks - .4, self.fracs[:Q], color=col)
          ax.set_xticks(ticks, map(lambda x: r"${}$".format(x), ticks + 1))
          ax.set_ylabel("Eigenvalue fraction")
          ax.set_xlabel("PC")
          ax.set_ylim(0, ax.get_ylim()[1])
          ax.set_xlim(ticks.min() - .5, ticks.max() + .5)
          try:
              pylab.tight_layout()
          except:
              pass
          return bar