Model parameters

Model parameters are implemented by GModelPar which derives from the abstract GOptimizerPar base class. Each model parameter is factorised into a value and a scale part according to

$$p=v\times s$$

where $p$ is the model parameter, $v$ is the model value factor, and $s$ is the model scale factor. All three components can be accessed or set via the GModelPar::value(), GModelPar::factor_value(), and GModelPar::scale() methods.

In addition, the class handles parameter errors and gradients as well as parameter minima or maxima. Parameter errors can be accessed or set via the GModelPar::error() and GModelPar::factor_error(), where the former concerns the error on $p$ while the latter concerns the error on $v$. Equivalent methods exist for the gradient (GModelPar::gradient() and GModelPar::factor_gradient()), the minimum (GModelPar::min() and GModelPar::factor_min()), and the maximum (GModelPar::max() and GModelPar::factor_max()).

Finally, GModelPar::fix() and GModelPar::free() methods allow to fix or to free a model parameter, and the GModelPar::is_free() and GModelPar::is_fix() methods allow to check whether a parameter is free or fixed.