optimflex: Derivative-Based Optimization with User-Defined Convergence Criteria

Provides a derivative-based optimization framework that allows users to combine eight convergence criteria.Unlike standard optimization functions, this package includes a built-in mechanism to verify the positive definiteness of the Hessian matrix at the point of convergence.This additional check helps prevent the solver from falsely identifying non-optimal solutions, such as saddle points, as valid minima.