Add chirp-mass and mass-ratio prior which are uniform in component masses

This MR is to implement the prior of mass ratio for the case where the uniform prior on component masses is applied while mass ratio is sampled.

The analytic expressions of its PDF and CDF are given in https://git.ligo.org/soichiro.morisaki/utilities/-/blob/master/mcq_sampling_bilby/mcqprior.pdf .

It has been tested in https://git.ligo.org/soichiro.morisaki/utilities/-/blob/master/mcq_sampling_bilby/CheckNewAnalyticPrior.ipynb .

cc: @colm.talbot

Thanks @soichiro.morisaki!

I added a few specific comments, there are two others that don't really fit at any specific line:

• This prior should live in the bilby/gw/prior.py module, rather than in core.
• I know I suggested the opposite before, but I think it would be beneficial to add a FlatInComponentsChirpMass class which is just a wrapper to the PowerLaw class.

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• 509c5793 - address Colm's comments on UniformInComponentsMassRatio

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• 7e03faa2 - add UniformInComponentsChirpMass

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• d24a175a - minor fixes

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• b91a0f3f - bilby/gw/prior.py: add UniformInComponentsChirpMass and UniformInComponentsMassRatio prior.

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• 70004ab2 - bilby/gw/prior.py: add UniformInComponentsChirpMass and UniformInComponentsMassRatio prior.

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unmarked as a Work In Progress

changed title from WIP: add mass-ratio prior to Add mass-ratio prior

changed title from Add mass-ratio prior to Add chirp-mass and mass-ratio prior which are uniform in component masses

@colm.talbot Thank you for the helpful comments! I believe I have addressed all of them and I have squashed the changes. The most updated prior has been tested in this notebook, and it works.

added Priors label

approved this merge request

This looks nice, is the idea that we just do

chirp_mass = UniformInComponentsMassRatio()
mass_ratio = UniformInComponentsChirpMass()
mass_1 = Constraint(...)
mass_2 = Constraint(...)

with the appropriate constraints?

From an implementation standpoint, I find the naming of the classes a little awkward, but I see the difficulty.

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• bccc0bd7 - bilby/gw/prior.py: add docstrings to UniformInComponentsChirpMass and UniformInComponentsMassRatio

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