ADR: ModelComponent

[henrikjacobsenfys]

ModelComponents

The basic building block of a model in EasyDynamcis is a ModelComponent. The following components exist:
Gaussian, Lorentzian, DeltaFunction, DampedHarmonicOscillator, Voigt, Polynomial and the base class ModelComponent. Each component lives in its own class.

Base class

The base class has unit, helpers to free and fix all the parameters and a method to convert input x (should be renamed to energy #72 ) to the proper format.

There is also a mixin to handle validation of input parameters. This will be simplified (#62 )

Components

Most components have an area, center and width property. area has been chosen over amplitude to facilitate easy convolution (#105 )
the width of a Gaussian is its standard deviation, $\sigma$, and the width of a Lorentzian is its half width at half maximum.

If center is not provided it will be set to 0 and fixed, as is appropriate for QENS analysis.

All components have an evaluate method which calculates the component values at the input x.

ComponentCollection

The ComponentCollection is the basic way to describe any model and is used extensively.
This is a collection of ModelComponent. I has the following methods:

• append_component: appends a component to the collection
• remove_component: removes a component by its unique_name
• normalize_area: normalizes the area of all components in the collection so they sum to 1. This is useful for convolutions
• evaluate: evaluates the sum of the components
• evaluate_component: evaluates a particular component
• is_empty: helper to check of the collection has any components or not

ComponentCollection was in its inception called SampleModel, and is discussed here: easyscience/dynamics#4