@article{10_4153_CMB_1963_004_9,
     author = {Swanson, C.A.},
     title = {Asymptotic {Variational} {Formulae} for {Eigenvalues}},
     journal = {Canadian mathematical bulletin},
     pages = {15--25},
     year = {1963},
     volume = {6},
     number = {1},
     doi = {10.4153/CMB-1963-004-9},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CMB-1963-004-9/}
}