@article{NUMA_1990__57_6-7_133434,
     author = {J\"urg T. Marti},
     title = {Small {Potential} {Corrections} for the {Discrete} {Eigenvalues} of the {Sturm-Liouville} {Problem.}},
     journal = {Numerische Mathematik},
     pages = {51--62},
     publisher = {mathdoc},
     volume = {57},
     number = {6-7},
     year = {1990},
     zbl = {0698.65051},
     url = {http://geodesic.mathdoc.fr/item/NUMA_1990__57_6-7_133434/}
}