Sanjeev Arora Eli Berger Elad Hazan Guy Kindler Muli Safra On Non-Approximability for Quadratic Programs Electronic Colloquium on Computational Complexity (ECCC) 2005 058 db/journals/eccc/eccc12.html#TR05-058 http://eccc.hpi-web.de/eccc-reports/2005/TR05-058/index.html