Fitting using third-party minimizers

[andped10]

General

The code should be able to fit the free parameters, P, of a model, m(P, x0), to determine the best possible match to some given experimental results, r(x0). The fitting code should allow for usage of various third-party codes capable of minimizing the difference between the model prediction, m(P,x0), and the expected result, r(x0), by determining for which P the objective function abs(m(P,x0) - r(x0)) is at a minimum.

To make different minimizers easily accessible in the code these should be fetched from a factory. For a minimizer to be in the factory it needs to inherit from the minimizer interface class, which enforces that the given minimizer implements a given set of methods. This then guarantees that a minimizer provided by the factory satisfies the minimizer interface and the factory can serve as the entry point from the fitter to any minimizers. Note that the fitter can only use methods defined in the minimizer interface.

To achieve this there are three levels of abstraction.

• Fitter what is exposed to our domain code.
• Minimizer wraps methods and translate data of a third-party code to make it usable by our Fitter.
• MinimizerEngine a third-party code that implements a given minimization algorithm(s). API is defined by and own by third-party.

The following lists the needed code parts.

Fitter

Single class.
It gets access to any of the supported MinimizerEngine from the MinimizerFactory
The Fitter is exchanging data with our domain model.

MinimizerFactory

Single class / function.
All contained Minimizer implements the interface defined by MinimizerBase.
It provides a requested Minimizer.

MinimizerBase

Single abstract class.
It defines the required interface methods expected by the Fitter.

Minimizer

Multiple classes.
It inherit from MinimizerBase.
It wraps a MinimizerEngine to expose the functionality that is required by the MinimizerBase.
It translates our domain data into a format that the given MinimizerEngine is able to used
It translates other input into something the given MinimizerEngine understand

• Constraints
• Parameters

It translates the data produce by the given MinimizerEngine into our domain

MinimizerEngine

Multiple classes.
This is a third-party python code with a given API.
It should be able to do a pip install or similar to pull the python code.