David Forrester Stephen G. Kobourov Armand Navabi Kevin Wampler Gary V. Yee Graphael: A System for Generalized Force-Directed Layouts. 454-464 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3383&spage=454 2004 conf/gd/2004 Graph Drawing db/conf/gd/gd2004.html#ForresterKNWY04