Hello I need help regarding sage math, since I cant find anything about it on the manuals.
So I have a function of the form $F(r,t) = 2r H(t)$ and then i want to perform an operation on it involving differentiation. H(t) is kept arbitrary. I know how to do this using sagemath. My question is, what if before performing any operation, I want to perform a change of variables $u = t-r$ and $v=t+r$ first? So my function now becomes
$F =(v-u) H( (u+v)/2)$
Is it possible to define H((u+v)/2) in sage math, such that when it takes the derivative it takes the partial derivative wrt u and then wrt v?