“…This convex hull characterization has led to the development of several techniques for problem (1) with general Q, including cutting plane methods [26,25], strong MISOCP formuations [1,32], approximation algorithms [56], specialized branching methods [34], and presolving methods [5]. Recently, problem (1) has been studied under other structural assumptions, including: quadratic terms involving two variables only [2,3,27,33,37], rank-one quadratic terms [4,6,51,50], and quadratic terms with Stieltjes matrices [7]. If the matrix can be factorized as Q = Q 0 Q 0 where Q 0 is sparse (but Q is dense), then problem (1) can be solved (under appropriate conditions) in polynomial time [21].…”