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I am trying to implement this problem in C language.

But in the mist, I don't even know what to start with.

Please tell me the knowledge to solve this problem, the domain that contains the knowledge, keywords etc.

I understand mathematical calculations and terminology.

In fact, when Θ = 0, the formula becomes simple, so the program was implemented and the calculation was completed.
Since then, it's ambiguous what I don't know to implement.
I want to gain at least ignorant knowledge ...

I would like to start studying from where I taught.