@article{NUMA_1970__15_132001,
     author = {H.A. LUTHER and H.G. SIERRA},
     title = {On the {Optimal} {Choice} of {Fourth-Order} {Runge-Kutta} {Formulas.}},
     journal = {Numerische Mathematik},
     pages = {354--358},
     publisher = {mathdoc},
     volume = {15},
     year = {1970},
     zbl = {0191.45101},
     url = {http://geodesic.mathdoc.fr/item/NUMA_1970__15_132001/}
}