@article{volkmer:2003:eer,
    author = {Volkmer, Hans},
     title = {Error estimates for {R}ayleigh-{R}itz approximations of
              eigenvalues and eigenfunctions of the {M}athieu and spheroidal
              wave equation},
   journal = {Constr. Approx.},
  fjournal = {Constructive Approximation. An International Journal for
              Approximations and Expansions},
    volume = {20},
      year = {2004},
    number = {1},
     pages = {39–54},
      issn = {0176-4276},
   mrclass = {33E10 (33F05 65F15)},
  mrnumber = {MR2025413 (2004m:33031)},
       doi = {10.1007/s00365-002-0527-9},
     zblno = {1063.33028}}