Suppose I do:
df(x, y) =
D(, f)(x, y)
Now I assign an expression to " f ", i.e.:
f(x,y) = y/x^2+x*y
f(x, y) =
x*y + y/x^2
My question is, how can I substitute " f " in " df "? The idea is to perform ther derivative automatically during substitution. Is this possible?
I have tried " subs ", " eval ", " compose ", direct substitution etc...
The problem seems to be that " df " has dependency on " x " and " y ", which makes sense, thus I am only able to make substitutions on " x " and " y " but " f ".
I know that I can assign the expression to " f " since the beginning, however that does not fit my application.