Exact and approximated solutions for the harmonic and anharmonic repulsive oscillators: Matrix method Braulio M. Villegas-Martínez, Héctor Manuel Moya-Cessa and Francisco Soto-Eguibar Eur. Phys. J. D, 74 7 (2020) 137 Published online: 01 July 2020 DOI: 10.1140/epjd/e2020-10128-2