# General information for adding new schemes¶

The following steps are required for any new options (such as new Hydrodynamics Schemes, chemistry, cooling, Equations of State, stars, or gravity)

In order to add a new scheme, you will need to:

1. Create a new subdirectory inside the option directory (e.g. src/equation_of_state or src/hydro) with an explicit name.
2. Create the required new files (depending on your option, you will need different files). Copy the structure of the most simple option (e.g. src/hydro/Gadget2, src/gravity/Default, src/stars/Default, src/cooling/none, src/chemistry/none or src/equation_of_state/ideal_gas)
3. Add the right includes in the option file (e.g. src/hydro.h, src/gravity.h, src/stars.h, src/cooling.h, src/chemistry.h or src/equation_of_state.h) and the corresponding io file if present.
4. Add the new option in configure.ac. This file generates the configure script and you just need to add a new option under the right case.
5. Add your files in src/Makefile.am. In order to generate the Makefiles during the configuration step, a list of files is required. In nobase_noinst_HEADERS, add your new header files.
6. Update the documentation. Add your equations/documentation to doc/RTD.