Nebular Emission 
**********
This section explains how we include nebular line emission within powderday. We use `CLOUDY <https://www.nublado.org/>`_ 
photoionization code for all our calculations. There are two different methods that are available for calculating nebular emission. 
These can be selected by setting *use_cloudy_tables* flag in parameters_master.py .

Lookup tables
--------------
If *use_cloudy_tables* is set to True, CLOUDY lookup tables (dev. by Nell Byler) that come pre-packaged with `FSPS <https://github.com/cconroy20/fsps>`_  
are used to calculate nebular emission.


Running CLOUDY (Under development)
--------------
If *use_cloudy_tables* is set to False, we calculate nebular emission by running CLOUDY for each young star particle. 
This makes the code slower but allows much more freedom over the model parameters. To use this option you 
need to have CLOUDY (version 17.00) installed on your machine. In order to install CLOUDY go this 
`link <https://nublado.org/wiki/StepByStep/>`_ and follow the step by step guide. 

Please make sure that you install *version 17.00*, using any other version may lead to errors or inconsistent results. 
Also, make sure that you have CLOUDY_EXE and CLOUDY_DATA_PATH environment variables set. CLOUDY_EXE should point
to the directory where your cloudy.exe is located. For CLOUDY version 17.00, this is inside the source folder within CLOUDY. 
Example: */home/desika.narayanan/c17.00/source/cloudy.exe*. CLOUDY_DATA_PATH should point to the CLOUDY data directory.
Example: */home/desika.narayanan/c17.00/data* 

**Note:** If for any reason the CLOUDY run crashes the code reverts back to using lookup tables for that star particle.

There are a whole host of parameters that you can change as per your need. A complete list of all the tunable parameters 
is described in the parameters description section.