A SEQUENTIAL QUADRATIC PROGRAMMING ALGORITHM FOR NONSMOOTH PROBLEMS WITH UPPER-C2 OBJECTIVE

An optimization algorithm for nonsmooth nonconvex constrained optimization problems with upper-C-2 objective functions is proposed and analyzed. Upper-C-2 is a weakly concave property that exists in difference of convex (DC) functions and arises naturally in many applications, particularly certain classes of solutions to parametric optimization problems e.g., recourse of stochastic programming and projection onto closed sets. The algorithm can be viewed as an extension of sequential quadratic programming (SQP) to nonsmooth problems with upper-C-2 objectives or a simplified bundle method. It is globally convergent with bounded algorithm parameters that are updated with a trust-region criterion. The algorithm handles general smooth constraints through linearization and uses a line search to ensure progress. The potential inconsistencies from the linearization of the constraints are addressed through a penalty method. The capabilities of the algorithm are demonstrated by solving both simple upper-C-2 problems and a real-world optimal power flow problem used in current power grid industry practices.