Wanpracha Art Chaovalitwongse Ioannis P. Androulakis Panos M. Pardalos Quadratic Integer Programming: Complexity and Equivalent Forms. 3153-3159 2009 Encyclopedia of Optimization http://dx.doi.org/10.1007/978-0-387-74759-0_536 reference/opt/2009 db/reference/opt/opt2009.html#ChaovalitwongseAP09