Effrosini Kokiopoulou Yousef Saad Orthogonal Neighborhood Preserving Projections: A Projection-Based Dimensionality Reduction Technique. 2143-2156 2007 29 IEEE Trans. Pattern Anal. Mach. Intell. 12 http://doi.ieeecomputersociety.org/10.1109/TPAMI.2007.1131 db/journals/pami/pami29.html#KokiopoulouS07