Nonconvex quadratically constrained programs (QCPs) are generally NP-hard and challenging problems. In this paper, we propose two novel mixed-integer linear programming (MILP) approximations for a nonconvex QCP. Our method begins by utilizing an eigenvalue-based decomposition to express the nonconvex quadratic function as the difference of two convex functions. We then introduce an additional variable to partition each nonconvex constraint into a second-order cone (SOC) constraint and the complement of an SOC constraint. We employ two polyhedral approximation approaches to approximate the SOC constraint. The complement of an SOC constraint is approximated using a combination of linear and complementarity constraints. As a result, we approximate the nonconvex QCP with two linear programs with complementarity constraints (LPCCs). More importantly, we prove that the optimal values of the LPCCs asymptotically converge to that of the original nonconvex QCP. By proving the boundedness of the LPCCs, we further reformulate the LPCCs as MILPs. We demonstrate the effectiveness of our approaches via numerical experiments by applying our proposed approximations to randomly generated instances and two application problems: the joint decision and estimation problem and the two-trust-region subproblem. The numerical results show significant advantages of our approaches in terms of solution quality and computational time compared with existing benchmark approaches. History: Accepted by Pascal Van Hentenryck, Area Editor for Computational Modeling: Methods & Analysis. Funding: K. Pan was supported in part by the Research Grants Council of Hong Kong [Grant 15503723]. J. Cheng and B. Yang were supported in part by the Office of Naval Research [Grant N00014-20-1-2154]. J. Cheng was supported in part by the National Science Foundation [Grant ECCS-2404412]. B. Yang was supported in part by the Air Force Office of Scientific Research [Grant FA9550-23-1-0508]. Supplemental Material: The software that supports the findings of this study is available within the paper and its Supplemental Information ( https://pubsonline.informs.org/doi/suppl/10.1287/ijoc.2024.0719 ) as well as from the IJOC GitHub software repository ( https://github.com/INFORMSJoC/2024.0719 ). The complete IJOC Software and Data Repository is available at https://informsjoc.github.io/ .

Knowledge graphs are vital for many tasks, including recommendation systems and node search. Learning to hash knowledge graph is to infer binary-vector representations of the graph. Compared with traditional knowledge graph embedding that learns continuous-vector representations, knowledge graph hashing could significantly reduce storage and computational time due to its binary nature. Despite the potential advantage, the problem of knowledge graph hashing is challenging due to the large-scale binary decision variables. In this article, we propose a novel discrete optimization framework for knowledge graph hashing. We treat the relations between heads and tails in the knowledge graph as element-wise rotation to learn binary codes. An alternating optimization algorithm is then proposed to produce high-quality code that captures knowledge graph information well. Furthermore, to obtain superior binary representations, we employ a dynamic range method during the alternating optimization process to adjust the approximations of the ReLU function \([x]_{+}\) . This ensures that valuable measures of dissimilarity are not overlooked, leading to more accurate computations. The evaluation results on five publicly available datasets demonstrate the superiority of the proposed algorithm against several state-of-the-art baseline methods.

Pseudolites can overcome the shortcomings of Global Navigation Satellite System(GNSS), and simulate similar navigation satellite signals to be used as a stable and reliable positioning signal source in the indoor environment, which has gradually become a research hotspot in the field of indoor positioning. Due to the influence of factors such as multipath propagation, it is impossible to directly replicate the existing outdoor positioning method. To solve the above problems, we designed a BDS/GPS array pseudolite indoor high-precision positioning system PIP's (Pseudolite Indoor Positioning system). Relying on this system, we proposed a pseudo-satellite carrier phase differential positioning algorithm based on particle filtering, which avoids the problem of solving the integer ambiguity by calculating the pseudorange similarity. Then, aiming at the problem of divergence of positioning results caused by different carrier moving speeds, a method of dynamically estimating particle velocity based on Doppler frequency shift is proposed, which improves the accuracy of particle weight distribution, thereby improving the positioning accuracy and continuity of the positioning system. Finally, in order to verify the positioning performance of the proposed system, we conducted a large number of experiments in the microwave anechoic chamber and the test field environment. The results show that in the microwave anechoic chamber, the average positioning error in the X direction is 0.09m, and the average positioning error in the Y direction is 0.12m. In the test field environment, we analyzed the influence of different transmitting powers and different types of antennas on the positioning performance. At the same time, the positioning accuracy heat map is drawn, and the maximum positioning error is 0.67m.

Distributionally robust optimization (DRO) is a modeling framework in decision making under uncertainty in which the probability distribution of a random parameter is unknown although its partial information (e.g., statistical properties) is available. In this framework, the unknown probability distribution is assumed to lie in an ambiguity set consisting of all distributions that are compatible with the available partial information. Although DRO bridges the gap between stochastic programming and robust optimization, one of its limitations is that its models for large-scale problems can be significantly difficult to solve, especially when the uncertainty is of high dimension. In this paper, we propose computationally efficient inner and outer approximations for DRO problems under a piecewise linear objective function and with a moment-based ambiguity set and a combined ambiguity set including Wasserstein distance and moment information. In these approximations, we split a random vector into smaller pieces, leading to smaller matrix constraints. In addition, we use principal component analysis to shrink uncertainty space dimensionality. We quantify the quality of the developed approximations by deriving theoretical bounds on their optimality gap. We display the practical applicability of the proposed approximations in a production–transportation problem and a multiproduct newsvendor problem. The results demonstrate that these approximations dramatically reduce the computational time while maintaining high solution quality. The approximations also help construct an interval that is tight for most cases and includes the (unknown) optimal value for a large-scale DRO problem, which usually cannot be solved to optimality (or even feasibility in most cases). Summary of Contribution: This paper studies an important type of optimization problem, that is, distributionally robust optimization problems, by developing computationally efficient inner and outer approximations via operations research tools. Specifically, we consider several variants of such problems that are practically important and that admit tractable yet large-scale reformulation. We accordingly utilize random vector partition and principal component analysis to derive efficient approximations with smaller sizes, which, more importantly, provide a theoretical performance guarantee with respect to low optimality gaps. We verify the significant efficiency (i.e., reducing computational time while maintaining high solution quality) of our proposed approximations in solving both production–transportation and multiproduct newsvendor problems via extensive computing experiments.

We propose a novel partial sample average approximation (PSAA) framework to solve the two main types of chance-constrained linear matrix inequality (CCLMI) problems: CCLMI with random technology matrix and CCLMI with random right-hand side. We propose a series of computationally tractable PSAA-based approximations for CCLMI problems, analyze their properties, and derive sufficient conditions that ensure convexity for the two most popular—normal and uniform—continuous distributions. We derive several semidefinite programming PSAA reformulations efficiently solved by off-the-shelf solvers and design a sequential convex approximation method for the PSAA formulations containing bilinear matrix inequalities. The proposed methods can be generalized to other continuous random variables whose cumulative distribution function can be easily computed. We carry out a comprehensive numerical study on three practical CCLMI problems: robust truss topology design, calibration, and robust control. The tests attest to the superiority of the PSAA reformulation and algorithmic framework over the scenario and sample average approximation methods. Summary of Contribution: In line with the mission and scope of IJOC, we study an important type of optimization problems, chance-constrained linear matrix inequality (CCLMI) problems, which require stochastic linear matrix inequality (LMI) constraints to be satisfied with high probability. To solve CCLMI problems, we propose a novel partial sample average approximation (PSAA) framework: (i) develop a series of computationally tractable PSAA-based approximations for CCLMI problems, (ii) analyze their properties, (iii) derive sufficient conditions ensuring convexity, and (iv) design a sequential convex approximation method. We evaluate our proposed method via a comprehensive numerical study on three practical CCLMI problems. The tests attest the superiority of the PSAA reformulation and algorithmic framework over standard benchmarks.