@article{RCM_2012_46_1_a1,
     author = {Jorge M. Ramirez},
     title = {Green's {Functions} for {Sturm-Liouville} {Problems} on {Directed} {Tree} {Graphs}},
     journal = {Revista colombiana de matematicas},
     pages = {15--25},
     publisher = {mathdoc},
     volume = {46},
     number = {1},
     year = {2012},
     url = {http://geodesic.mathdoc.fr/item/RCM_2012_46_1_a1/}
}