Optimal q-homotopy analysis method for time-space fractional gas dynamics equation K. M. Saad, E. H. AL-Shareef, Mohamed S. Mohamed and Xiao-Jun Yang Eur. Phys. J. Plus, 132 1 (2017) 23 Published online: 19 January 2017 DOI: 10.1140/epjp/i2017-11303-6