@Scot Gould Thanks for the detailed answer!
Of course this was just a simple example of the problem, and to restate my issue:
what i often require is a way to define a new function which has the derivative of a previously defined fucntion as a part of it, say
f(x,y) = d/dx g(x) * y
and then later evaluate f(2,3) or so, expecting the d/dx to act as an operator rather than keeping "x" as a variable, and trying to evaluate f(2,3) = d/d2 g(2)*3.
This may simply be a fault of my previous experience with math programs like Maple, especially since im not used to seeing the
g:= x->( d/dx f(x) )
But intuitively, f(x) is assigned a "static" function first calculated as the derivative of g, then assigned to f as a string, not related to the d/dx operator any longer.
This of course breaks the functionality of S(i,j) = d/dui (expression) + d/duj(other expression).
>>I couldn't help but notice that the document you provided is written in "worksheet mode" as opposed to document mode. Does this matter for the demonstration, or do i simply lack the knowledge of how to the |x=x1 operation?