@article{NUMA_1989__54_3_133338,
     author = {Peter Zitnan},
     title = {An a posteriori {Error} {Estimation} of the {Rayleigh-Ritz} {Eigenvalues.}},
     journal = {Numerische Mathematik},
     pages = {639--654},
     publisher = {mathdoc},
     volume = {54},
     number = {3},
     year = {1989},
     zbl = {0645.65027},
     url = {http://geodesic.mathdoc.fr/item/NUMA_1989__54_3_133338/}
}