Chun Hung Li Zhi-Li Wu Spectral Energy Minimization for Semi-supervised Learning. 13-21 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3056&spage=13 2004 conf/pakdd/2004 PAKDD db/conf/pakdd/pakdd2004.html#LiW04