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Guidelines for the Implementation of Different Dark Energy Models in CLASS

1. Download the latest version of CLASS from the official GitHub repository.
2. In section 8a of the explanatory.ini file, fix Omega_Lambda, and Omega_scf equal to zero, in order to avoid any contribution from the cosmological constant or a scalar field, and comment out the option Omega_fld.
3. Enter the include folder.
4. Locate the background.h file, and specify inside the struct background loop the variable type of the considered dark energy model.
5. Enter the source folder.
6. In the file background.c include any necessary extra libraries, and either include a new section in the code with your model (similar to those implemented for the default parametrizations), or modify the functions *w_fld, *dw_over_da_fld and *integral_fld of the default CPL model for simplicity.
7. In the input.c file inside the if(pba→fluid_equation_of_state=”model_name”) routine include the dark energy variables, and in the section background structure store the default values of the extra parameters of your dark energy model. 

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