It can be convenient not to handle the optimized parameters as elements
of a vector, but as named fields of a structure. The frontends
nonlin_residmin, nonlin_curvefit, residmin_stat,
curvefit_stat, and nonlin_min can accept parameter
information in structure form, and can pass the parameters as a
structure to user functions, although the backends still handle the
parameters as vectors.
To use this feature, the initial parameters must be given in structure
form, or the setting param_order must be given, a cell-array with
names of the parameters. If both is done, only the parameters in
structure fields named in param_order will be optimized. If
there are still some non-structure-based configuration settings or user
functions, specifying param_order is mandatory even if the
initial parameters are given in structure form.
If the initial parameters are a structure, the parameters being the optimization result will also be returned as a structure.