How to use ∂ function in my code or how to compute the mixed second-order partial derivatives or first-order cross partial derivatives of the velocity field **u**?

[nilshg]

Are you doing this as part of a university course or something? The same question was asked yesterday:

How to use partial derivate in my code?

If you just want to know how to type it, the REPL help tells you: help?> ∂ "∂" can be typed by \partial<tab> This kind of tab completion is supported in the REPL and can also be configured in most modern editors. But by default, ∂ doesn’t have any definition in Julia, and is just another possible identifier, like x or f. It is up to you to assign a meaning to it.