COOLEST support in lenstronomy

[ajshajib]

It would be convenient to have a feature that packs (and loads) the common dictionaries, lists, kwargs_data, kwargs_psf, etc. created/used during modeling into a file in the COOLEST format. @LyneVdV informed me that she already has some code that performs this task. 🙏 We can discuss here to figure out where to add such code within lenstronomy (e.g., Util?), and what would be the requirements/requests for this feature.

[sibirrer]

great idea! Perhaps it can go into Util.param_util?

[aymgal]

Thanks for starting the discussion @ajshajib !

Let me simply add some details about the role of the standard we developed:

• A lensing system stored in the COOLEST standard is composed of a directory, whose main component is a single JSON template file recording (in the most "code-independent" way possible) most of the quantities that define a lensing system and its model. This includes the different galaxies (instead of lensing planes), external shear components, associated parameter values and/or priors, instrumental and noise properties, etc. The fact that it is a directory is that it allows to store external files along with the JSON template, such as FITS files for the data, noise maps, etc., as well as MCMC chains for instance.
• Another part of COOLEST is an API with plotting routines, functions to compute effective quantities and model comparisons. But this is probably not the part of the standard which is interesting for us here.

Although any code-dependent container (such as lenstronomy's kwargs) cannot (and should not) be stored as it is in the JSON template, there is a specific field 'meta' (for metadata) in the template which exactly suits this purpose. For example, one can add a link (i.e. just the file name) to a pickled file containing all lenstronomy's kwargs.

Then, on top of @LyneVdV's routines that fill in the JSON template based on lenstronomy's setup, one could add additional metadata that directly packs all kwargs or missing information (I am thinking about numerics settings for instance). What do you think? Let me know if something is unclear.

[LyneVdV]

I added my routines in the PR #465 and its content is also discussed in the issue #452 :) ! I created new files in the Util folder. If you think it should belong somewhere else or be part of other existing files, let me know !