(calibration_classes_functions_observations)=
# Calibration classes, distance and likelihood functions, observations and model

This section introduces the common elements of all analyses in the **Calibration** module. Indeed the 
methods discussed hereafter will be using the same architecture and will require a common set of items, 
listed below:

- a model has to be set up as this is what one wants to calibrate. It can come either as a 
`Relauncher::TRun` instance, as a `Launcher::TCode` or a **Launcher** function. This part is 
introduced in [](#calibration_classes_functions_observations_data_model) (for the general concept and 
the difference with the usual organisation of model definition) and discussed later on (mainly in relation 
to the constructor of `TCalibration`-derived objects) in 
[](#calibration_classes_functions_observations_calibration_classes) and in the dedicated section in 
each method;

- a reference observations have to be defined once and for all so that the model can be run for 
each newly defined set of parameter values (every new configuration). This part is discussed first 
in [](#calibration_classes_functions_observations_data_model) and the way to provide them is also partly 
discussed in [](#calibration_classes_functions_observations_data_and_distance);

- a distance or likelihood function has to be created, usually within the calibration instance, to quantify how well 
the model under study reproduces the reference observations. This part is 
discussed in [](#calibration_classes_functions_observations_data_and_distance);

- a main object has to be created, a calibration method instance, that inherits from the 
`TCalibration` class. This is discussed in 
[](#calibration_classes_functions_observations_calibration_classes).

```{toctree}
classes_functions_observations/data_model
classes_functions_observations/data_and_distance
classes_functions_observations/calibration_classes
classes_functions_observations/use_case
```