I have a problem about derivative expression... I use T as a variable in the Partial Differential Equations model, when I check my results, I find that Tx≠0, while d(T,x)=0. Why this happen? And if I want to get other derivation G, which couldn't be written as Gx, how can I deal with that? (I calculate and find d(G,x)=0, but it isn't right)
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