## 2 Functions for optimization of a model function returning an array

Model functions whose parameters are to be optimized may return a vector or array of values. Either these or their differences to some constant values (curve fitting) can be minimized in some sense, often, but not necessarily, by minimizing the sum of their squares. It is usually preferable to use optimizers designed for residual optimization for this purpose. These can exploit information contained in the individual elements of the returned array, which would not be possible if the user calculated a norm (e.g. sum of squares) of the elements and performed a scalar optimization.