Exact and approximated solutions for the harmonic and anharmonic repulsive oscillators: Matrix methodBraulio M. Villegas-Martínez, Héctor Manuel Moya-Cessa and Francisco Soto-EguibarEur. Phys. J. D, 74 7 (2020) 137DOI: https://doi.org/10.1140/epjd/e2020-10128-2