@article{NUMA_1990__58_5_133488,
     author = {Jan Mandel},
     title = {On block diagonal and {Schur} complement preconditioning.},
     journal = {Numerische Mathematik},
     pages = {79--94},
     publisher = {mathdoc},
     volume = {58},
     number = {5},
     year = {1990},
     zbl = {0687.65036},
     url = {http://geodesic.mathdoc.fr/item/NUMA_1990__58_5_133488/}
}