Question: Isolate differentiation


I have an expression and want to find its derivative respect to T[1] but not T[2], for example: 

u[1](T[1], T[2], T[3]):=exp(T[1]*I)

If I find the 

diff(u[1](T[1], T[2], T[3]), T[1], T[2])

I would like to get something like this:

D__1*diff(u[1](T[1], T[2], T[3]), T[1])

instead of the derivative respect to T[2], which makes the result to be zero.

I need an expression that I can do other things with it.

You might say why do you just remove the diff of T[2], well I want to automate my code and this is part of the expression so I cannot write something else.



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