Bomze, I. M., L. Grippo, and L. Palagi. “Unconstrained Formulation of Standard Quadratic Optimization Problems”. Department of Computer and System Sciences Antonio Ruberti Technical Reports, vol. 2, no. 12, Oct. 2010, p. 16, https://rosa.uniroma1.it/rosa00/index.php/dis_technical_reports/article/view/8902.