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## Summary:

- How to derive the finite difference derivative formulation from the natural boundary formulation?

## Main Question or Discussion Point

*PS: This is not an assignment, this is more of a brain exercise.*

I intend to apply a general derivative boundary condition f(x,y). While I know that the boxed formulation is correct, I have no idea how to acquire the same formulation if I come from the general natural boundary condition formulation. I honestly do not know what am I doing wrong. Can someone check where am I incorrect?