Deng Cai Xiaofei He Xuanhui Wang Hujun Bao Jiawei Han Locality Preserving Nonnegative Matrix Factorization. 1010-1015 2009 IJCAI http://ijcai.org/papers09/Papers/IJCAI09-171.pdf conf/ijcai/2009 db/conf/ijcai/ijcai2009.html#CaiHWBH09