There is a typographical error in our recently published paper (Kourakis et al. 2014), namely, in the algebraic expression for the quantity C210 provided in the Appendix.

The correct expression for C210 should read:

${C}_{2_1}^0=\frac{c_1\left(\frac{c_1+k^2}{b}\right)^2\left(\frac{2v_g\omega}{k}+\frac{\omega^2}{k^2}\right)-2ac_2}{c_1v_g^2-ab} \, .\$

The modification is limited to the presentation of the algebraic calculation, hence the plots presented in the paper are not affected by the typographical error.