On SOCP/SDP formulation of the extended trust region subproblem

In this paper, we consider the extended trust region subproblem (\eTRS) which is the minimization of an indefinite quadratic function subject to the intersection of unit ball with a single linear inequality constraint. Using a variation of S-Lemma, we derive the necessary and sufficient optimality conditions for \eTRS. Then an SOCP/SDP formulation is introduced for the problem. Finally, several illustrative examples are provided.