Clarify role of required init vars

[vgro]

The question came up what exactly needs to go in the required_init_vars of a model to ensure that the dummy simulation runs. Is it all the input variables needed to run the model or only the ones that come from somewhere external, like ERA5 data?

[davidorme]

I think we probably need to discriminate between these two things. I think this is going to be at the heart of any attempt to freeze modules - some data has to be provided to start the model running, but others are generated from those. It's linked to the idea of what variables are provided by which module.

[vgro]

Ok, so I include all the inputs that the model expects to run

[davidorme]

That it needs to __init__. I think in the near future we may end up defining all of these variables in their own register and provide a resolution process of which variables are populated by which models and which need to be provided etc.

[davidorme]

@dalonsoa - this is linked to #388. We might want to split required_init_vars into required_config_data and required_init_vars? It would be useful in the variable docs to be very clear about what data must be provided as an input and at the moment cannot be seen from required_init_vars. I guess we could work it out from required_init_vars and a new vars_initialised property across models, but it seems cleaner to be explicit!

[vgro]

resolved with #388