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1.2 Default backend lm_feasible of scalar optimization

A Levenberg/Marquardt-like algorithm, attempting to honour constraints throughout the course of optimization. This means that the initial parameters must not violate constraints (to find an initial feasible set of parameters, e.g. core Octaves sqp can be used ( see octave_sqp), by specifying an objective function which is constant or which returns a norm of the distances to the initial values). The Hessian is either supplied by the user or is approximated by the BFGS algorithm. Core Octaves sqp performed better in some tests with unconstrained problems.

Returned value cvg will be 2 or 3 for success and 0 or -4 for failure ( see nonlin_min for meaning). Returned structure outp will have the fields niter, nobjf, and user_interaction.

Backend-specific defaults are: MaxIter: 20, fract_prec: zeros (size (parameters)), max_fract_change: Inf for all parameters. The setting TolX is not honoured.

Interpretation of Display: if set to "iter", currently only information on applying max_fract_change is printed.