Organize and reorder utils for Kerr, Kerr-Newman and Schwarzschild metrics

🐞 Problem As of now, various useful functions used by metric/schwarzschild.py are in utils/schwarzschild_utils.py. Same goes for metric/kerr.py and metric/kerrnewman.py. We need to move these functions out of utils and make them a core part of library as they are quite-useful even when used stand-alone.

🎯 Goal

• Migrate them somewhere, so as to make them look like a core part of library.
• Reorder the parameters inside the functions, so as parameters like c, G etc are made to be optional with default values can be taken in SI units from constant.py.
• Many functions take Rs as parameters which is Schwarzschild Radius. However, there is no sense to keep parameters Rs as it can be calculated from more fundamental things like mass, speed of light(c), gravitational constant(G). Rs = 2*M*G/square(c).
• These changes would break the API, and therefore requires updation of tests and example notebooks.

⏫ Progress

The tasks to be taken up in separate PRs

• Reorder parameters within functions
• Move the functions somewhere more suitable

💡 Possible solutions

• Firstly, wherever the functions take Rs, i.e schwarzschild radius as an input, replace them with M,G, and c and calculate Rs = 2*G*M/(c**2) inside the function itself. We can’t expect the user to supply schwarzschild radius. While implementing it, leave out function delta() in both kerr_utils.py and kerrnewman_utils.py.

• Currently functions are like func(c, G, Cc, r, theta.....). Here the fundamental constants need to be optional arguments and therefore, should be last few parameters like func(r, theta, ..... , c=default_value, G=default_value, Cc=default_value). Leave out G and Cc whenever not required.

  • c is Speed of light. Default value : einsteinpy.constant.c.value
  • G is gravitational constant. Default value : einsteinpy.constant.G.value
  • Cc is coulomb’s constant. Default value : einsteinpy.constant.coulombs_const.value

• After the changes, the API would break, therefore, update the example notebooks.

• Update the user guide

• Update the tests

📋 Steps to solve the problem

• Comment below about what you’ve started working on.
• Add, commit, push your changes
• Submit a pull request and add this in comments - Addresses #141
• Ask for a review in comments section of pull request
• Celebrate your contribution to this project 🎉

[ritzvik]

i thought of making a module “core.py” and putting the functions in there. is it fine? or can you suggest something better?

@alpeshjamgade Reorganizations is also being undertaken in the core metric modules in PR #203 . We have to wait for a while to work on this. I’ll notify when the time is right 😃 . BTW thanks for taking this up.

[JeS24]

Almost all of the utilities have been moved into metric itself, in #512.