@article{NUMA_1971__18_132120,
     author = {K.P. Hadeler},
     title = {Bemerkungen zum {Gradientenverfahren.}},
     journal = {Numerische Mathematik},
     pages = {413--422},
     publisher = {mathdoc},
     volume = {18},
     year = {1971},
     url = {http://geodesic.mathdoc.fr/item/NUMA_1971__18_132120/}
}