Erich Kaltofen Bin Li Zhengfeng Yang Lihong Zhi Exact certification of global optimality of approximate factorizations via rationalizing sums-of-squares with floating point scalars. 155-164 2008 ISSAC http://doi.acm.org/10.1145/1390768.1390792 conf/issac/2008 db/conf/issac/issac2008.html#KaltofenLYZ08