Plots reaction energy as a function of mixing ratio x in
        self.c1 - self.c2 tie line using pylab.

        Returns:
            Pylab object that plots reaction energy as a function of
            mixing ratio x.

def plot(self):
        """
        Plots reaction energy as a function of mixing ratio x in
        self.c1 - self.c2 tie line using pylab.

        Returns:
            Pylab object that plots reaction energy as a function of
            mixing ratio x.
        """
        plt.rcParams['xtick.major.pad'] = '6'
        plt.rcParams['ytick.major.pad'] = '6'
        plt.rcParams['axes.linewidth'] = 2
        npoint = 1000
        xs = np.linspace(0, 1, npoint)

        # Converts sampling points in self.c1 - self.c2 tie line to those in
        # self.comp1 - self.comp2 tie line.
        xs_reverse_converted = InterfacialReactivity._reverse_convert(
            xs, self.factor1, self.factor2)
        energies = [self._get_energy(x) for x in xs_reverse_converted]
        plt.plot(xs, energies, 'k-')

        # Marks kinks and minimum energy point.
        kinks = self.get_kinks()
        _, x_kink, energy_kink, _, _ = zip(*kinks)
        plt.scatter(x_kink, energy_kink, marker='o', c='blue', s=20)
        plt.scatter(self.minimum()[0], self.minimum()[1], marker='*',
                    c='red', s=300)

        # Labels kinks with indices. Labels are made draggable
        # in case of overlapping.
        for index, x, energy, _, _ in kinks:
            plt.annotate(
                index,
                xy=(x, energy), xytext=(5, 30),
                textcoords='offset points', ha='right', va='bottom',
                arrowprops=dict(arrowstyle='->',
                                connectionstyle='arc3,rad=0')).draggable()
        plt.xlim([-0.05, 1.05])
        if self.norm:
            plt.ylabel('Energy (eV/atom)')
        else:
            plt.ylabel('Energy (eV/f.u.)')
        plt.xlabel('$x$ in $x$ {} + $(1-x)$ {}'.format(
            self.c1.reduced_formula, self.c2.reduced_formula))
        return plt