Tracking changes in isotopic content of grid

[miaoL1]

I notice that Stammler has already studied "How fragmentation impacts dust filtering by planets", which is related to NN and CN dichotomy. However, I find it knotty to directly track how isotopic changes in the grid along with the evolution of mass bin.

Since the calculation of the changes in the mass bin has already been encapsulated and changes of isotopic correspond to mass bin, I'm not sure if simply adding a subgroup to Grid can achieve this purpose.

I'm not sure if there's a better alternative yet.

[stammler]

Tracking additional parameters (like isotopic composition, porosity, etc.) is unfortunately more complex since it has to take coagulation into account (see Okuzumi et al., 2009; Stammler et al., 2017). It would require to solve the coagulation equation for every additional parameter plus advection (plus potential evaporation/chemistry). This is not implemented in the current version of DustPy, yet, but it is definitely on the roadmap and under development.

Stammler et al. (2019) were only looking at the total mass budget to investigate the permeability of gap, but not looking at detailed compositions.

For scientific discussions I would like to refer to Github discussion.