Add a few special metrics in symbolic module

🐞 Problem Yes, I’m talking about Schwarzschild metric & possibly, Kerr metric.

💡 Possible solutions

• These can be separate classes inheriting from Metric class, or just functions returning an object of the Metric class. Open to discussion

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[OVSofia]

I do it like this

[ritzvik]

In my opinion the best option is the second (Just functions). But why they shouldn’t be functions of the class ChristoffelSymbols(Tensor) ? (That’s how I did it)

That’s what I was thinking, functions are best. They should be functions returning instances of MetricTensor(Tensor) and not be functions inside the class, so that the classes do not lose their generality.