Optimization Framework
Iterative algorithms solve constrained non-linear problems by restricting the step size to a neighborhood where a local approximation is valid. The trust-region reflective method defines this localized area and adjusts it dynamically based on the model’s accuracy.
Bound Handling
When a proposed optimization step crosses a parameter limit, the algorithm uses reflection to redirect the step back into the feasible region. This reflective technique prevents the trust-region reflective routine from evaluating points outside the allowed boundaries. By reflecting the search path off the constraint boundaries, the solver continues to explore the interior of the feasible parameter space.
This approach avoids the computational failures that occur when evaluating undefined functions.
Iteration Control
Quadratic models approximate the objective function within the trust region to find a candidate minimizer. If the actual reduction matches the predicted reduction, the trust-region reflective algorithm expands the region size for the next step. A poor match causes the algorithm to shrink the region and re-evaluate the step with a smaller step size.
This dynamic adjustment ensures stable progress toward the minimum even on steep or irregular surfaces.
Scalability Limit
High-dimensional problems with thousands of constraints require significant processing time to compute the reflective boundary intersections. The trust-region reflective algorithm requires solving a system of linear equations at each iteration, which can bottleneck large-scale calculations. Approximations such as preconditioned conjugate gradients are used to handle these large matrices efficiently.
If the objective function is highly non-continuous, the solver may still struggle to locate the true global minimum.