ENH: Add a mass sampler for the colossus halo mass function

[sutieng]

Description

We add a new feature to sample halos from colossus halo mass function.

Checklist

• Follow the Contributor Guidelines
• Write unit tests
• Write documentation strings
• Assign someone from your working team to review this pull request
• Assign someone from the infrastructure team to review this pull request

[rrjbca]

Looks good so far. A few suggestions to generalise the function and make it more useful. I would also suggest:

• This file should be in the halos directory and renamed. I suggest git mv skypy/clusters/sampler.py skypy/halos/_colossus.py.
• Update the docstring and docs/halos/index.rst to ensure the new function appears in the documentation
• Write some unit tests. Perhaps look at the tests for schechter_lf_magnitude as that is quite a similar function

If you need help with any of this just ask

[Lucia-Fonseca]

• Agreed with @rrjbca 's comments.
• Please, check the flake8 style error messages.
• Can you add the equation number in Dispali+16 as a reference?

[rrjbca]

Would it be reasonable to refer to the objects sampled by this function as "halos" rather than "clusters" throughout the docstrings here? i.e. are "clusters" simply "high-mass halos" in this context?

[rrjbca]

@sutieng could you please add a "Description" for this pull request? We also need to write some unit tests and integrate the function docstring into the documentation, are you able to do these or would you like one of us to help?

[sutieng]

Would it be reasonable to refer to the objects sampled by this function as "halos" rather than "clusters" throughout the docstrings here? i.e. are "clusters" simply "high-mass halos" in this context?
Yes, I agree. Since here we are only considering DM component, so cluster can be referred to high mass halos. I will make changes of the docstrings.

[sutieng]

@sutieng could you please add a "Description" for this pull request? We also need to write some unit tests and integrate the function docstring into the documentation, are you able to do these or would you like one of us to help?
I don't have experience on writing unit tests. It would be great if you could help and let me know what items/ tests are needed to be included in unit tests.

[rrjbca]

Thanks for writing the tests and documentation they look great. Just a few suggestions:

• Move imports and skip unit test to avoid an ImportError if colossus is not installed
• Make sure to install colossus on ReadTheDocs
• Also test the maximum value and the shape of the samples

[rrjbca]

Excellent, the tests are running and the documentation is building now. Just a couple of small final changes:

• If you look at the documentation here you can see some parts have not rendered correctly, mostly due to whitespace and units. See suggestions for how to improve this.
• Since this is your first contribution could you add your details to .zenodo.json as a creator

[rrjbca]

Looks good to me, thank you for working on this @sutieng

[Lucia-Fonseca]

This works perfectly.
Great job @sutieng!