Sentence:  Tawarmalani and Sahinidis (2001) developed the <WSD>convex envelope</WSD> and concave envelope for "x"/"y" over a unit hypercube, compared it to the convex relaxation proposed by Zamora and Grosmmann (1998a), (1998b), (1999), proposed a semidefinite relaxation of "x"/"y", and suggested <WSD>convex envelopes</WSD> for functions of the form "f"("x")"y"2 and "f"("x")/"y". 
Meaning of the word marked with <WSD> tags:  For a given set S\subseteq\mathbb{R}^n and real-valued function "f" defined on the convex hull conv("S"), the highest-valued convex function that underestimates or equals "f" over "S".