@article{GDZPPN002211173,
title = {Approximation of isolated eigenvalues of ordinary differential operators.},
journal = {Journal f\"ur die reine und angewandte Mathematik},
volume = {435},
year = {1993},
pages = {31-44},
zbl = {0781.34052},
url = {http://dml.mathdoc.fr/item/GDZPPN002211173}
}
Stolz, Günter; Weidmann, Joachim. Approximation of isolated eigenvalues of ordinary differential operators.. Journal für die reine und angewandte Mathematik, Tome 435 (1993) pp. 31-44. http://gdmltest.u-ga.fr/item/GDZPPN002211173/