Optimal analytic method for the nonlinear Hasegawa-Mima equation Mathew Baxter, Robert A. Van Gorder and Kuppalapalle Vajravelu Eur. Phys. J. Plus, 129 5 (2014) 98 Published online: 29 May 2014 DOI: 10.1140/epjp/i2014-14098-x