New classes of anisotropic models with generalized polytropic equation of state S. A. Mardan, I. Noureen, M. Azam, M. A. Rehman and M. Hussan Eur. Phys. J. C, 78 6 (2018) 516 Published online: 22 June 2018 DOI: 10.1140/epjc/s10052-018-5992-9