# 3. The Cosmology calculator¶

Starting with version 1.1, there is now a module available that makes it easy for the user to perform calculations on the background cosmology given a specific model. A few classes of models are predefined. Each of these have also defined what are their components, but also allowing some variations. For example, the $$\Lambda\text{CDM}$$ model requires at least cold dark matter (cdm) and cosmological constant (lambda), but one can also include baryonic fluid (baryons), or treat both matter components together by specifying the composed species matter. It is also possible to include photons or radiation. For models of interaction between dark matter and dark energy (cde), the former is labelled idm and the latter ide or ilambda in the case that its equation-of-state parameter is still $$-1$$ (in which the model is then labelled cde_lambda) rather than a free parameter or presents evolution described by some function. The models available and their components specification are defined in the file EPIC/cosmology/model_recipes.ini. The fluids contained in this file are in turn defined in EPIC/cosmology/available_species.ini, where properties like the type of equation of state, the parameters and other relevant informations are set.

In version 1.2, a graphical user interface (GUI) for this cosmology calculator has been added to EPIC. After describing how all calculations are done in EPIC, we present the GUI in the last section.