@article{NUMA_1974__23_132301,
     author = {F. Chatelin and M.J. Lemordant},
     title = {La m\'ethode de {Rayleigh-Ritz} appliqu\'ee \`a des op\'erateurs diff\'erentiels elliptiques {\^A?} orders de convergence des \'el\'ements propres.},
     journal = {Numerische Mathematik},
     pages = {215--222},
     publisher = {mathdoc},
     volume = {23},
     year = {1974},
     zbl = {0295.65060},
     url = {http://geodesic.mathdoc.fr/item/NUMA_1974__23_132301/}
}