%0 Journal Article %A V. A. Sadovnichii %A V. E. Podolskii %T A class of Sturm–Liouville operators and approximate calculation of the first eigenvalues %J Sbornik. Mathematics %D 1998 %P 129-145 %V 189 %N 1 %U http://geodesic.mathdoc.fr/item/SM_1998_189_1_a6/ %G en %F SM_1998_189_1_a6