@article {femsupptree,
	title = {Solving Elliptic Finite Element Systems in Near-Linear Time with Support Preconditioners},
	journal = {SIAM J. Numer. Anal.},
	volume = {46},
	year = {2008},
	pages = {3264-3284},
	author = {E. Boman and B. Hendrickson and S. Vavasis}
}