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Rohan Rele

Publications and source records attributed to Rohan Rele.

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A Certificate of Unboundedness for Polynomial Optimization Problems

Global polynomial optimization methods typically rely on compactness of the feasible region in order to find solutions. These methods can incur considerable computational expense and most commercially available solvers do not verify the existence of a solution prior to undergoing global search. In this manuscript we propose a simple pre-processing algorithm to determine if an arbitrary polynomial optimization problem is unbounded from below thereby providing information about the problem's asymptotic geometry prior to solving the problem if a solution can be found.

math.OC

A Stochastic Record-Value Approach to Global Simulation Optimization

Black-box optimization is ubiquitous in machine learning, operations research and engineering simulation. Black-box optimization algorithms typically do not assume structural information about the objective function and thus must make use of stochastic information to achieve statistical convergence to a globally optimal solution. One such class of methods is multi-start algorithms which use a probabilistic criteria to: determine when to stop a single run of an iterative optimization algorithm, also called an inner search, when to perform a restart, or outer search, and when to terminate the entire algorithm. Zabinsky, Bulger & Khompatraporn introduced a record-value theoretic multi-start framework called Dynamic Multi-start Sequential Search (DMSS). We observe that DMSS performs poorly when the inner search method is a deterministic gradient-based search. In this thesis, we present an algorithmic modification to DMSS and empirically show that the Revised DMSS (RDMSS) algorithm can outperform DMSS in gradient-based settings for a broad class of objective test functions. We give a theoretical analysis of a stochastic process that was constructed specifically as an inner search stopping criteria within RDMSS. We discuss computational considerations of the RDMSS algorithm. Finally, we present numerical results to determine its effectiveness.

math.OC

On existence of solutions to non-convex minimization problems

We provide a unified framework for a systematic analysis of the existence of solutions to general nonconvex problems, relying on asymptotic and retractive cones for functions and sets. Using this framework we develop new necessary and sufficient conditions for the existence of solutions to a general problem of minimizing a proper closed function over a closed, possibly unbounded, set. Towards the result, we introduce cones of retractive directions for a set and a function, establishing some basic properties for them. We also investigate the relationships between the cone of retractive directions of a function and the cone of level sets of the function. Using the cones of retractive directions we provide necessary and sufficient conditions for the existence of solutions that require an asymptotically bounded decay of a function, and a relation between the cones of retractive directions of the constraint set and the asymptotic cone of the objective function. Finally we refine these conditions for more structured problems.

math.OC