Lecture #1 [Supowit and Reingold 1983] The complexity of drawing trees nicely
This paper shows that one can use LP-based methods to minimize the width of a "balanced-layered" drawing of tree, but if one desires a grid drawing the problem becomes NP-hard.
Clique na hiperligação http://link.springer.com/article/10.1007%2FBF00289576 para abrir o URL.