PORT 3 subroute library

The nonlinear optimizers use trust-region algorithms. Gradients/Jacobians can be either provided by the caller or approximated automatically by finite differences. The general minimization routines use either a quasi-Newton approximation to the Hessian matrix or a Hessian provided by the caller; the nonlinear least-squares routines adaptively switch between the Gauss-Newton Hessian approximation and an "augmented" approximation that uses a quasi-Newton update. Function and, if necessary, gradient values may be provided either by subroutines or by reverse communication.