I'd like to know if there's a way of declaring functions in sage that are as-yet unknown. For example, let's say I have a function
p = R*T/v - a(T)/v/(v+b)
And I would like to be able to take a derivative like this
and be given something back a partial derivative something like
R/v - diff(a(T),T)/v/(v+b)
However at present I can't seem to put an abstract function
a(T) into my expression or find anything in the documentation that says how this is done.
As I recall there was a way to do this with wxMaxima, so maybe I just haven't found the trick in Sage yet.