Comment #20 on issue 1816 by renato.c...@gmail.com: Adding partial
derivatives and taking derivatives with respect to functions
http://code.google.com/p/sympy/issues/detail?id=1816
I don't think what's being implemented is the Frechet derivative. For
example:
http://www.wolframalpha.com/input/?i=Frechet+derivative+of+cos%28x%29+wrt+exp%28x%29
[this says: cos(x).diff(exp(x)) = exp(x)]
The issue topic looks more like a simple partial derivative, as is very
commonly used in mechanics. That is, you treat df(x(t), x'(t), t)/dx'(t) as
if x' were a variable, not a function, and carry on the usual derivative.
At this point, usually x and x' are mere symbols, without an actual
("named") function attached to them.
The problem for me is still with named functions. In my mechanics courses I
never had to take any derivatives like diff(cos(x), sin(x)), so I would
really like to see a practical example where this is useful and a clearer
definition of what that means.
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