"Overview". Columbia University Department of Industrial Engineering and Operations Research. Diarsipkan dari versi asli tanggal 2012-07-17. Diakses tanggal 2012-07-22.
"Overview". Columbia University Department of Industrial Engineering and Operations Research. Diarsipkan dari versi asli tanggal 2012-07-17. Diakses tanggal 2012-07-22.