Hi everybody,
I've got a function u depending on a variable x. So I declared:
(%i1) depends(u,x);
I now want to differentiate u with respect to x. So:
(%i2) diff(u,x);
Now I want to substitute the independent variable x with l*X, where l
is a constant parameter. What I want to obtain is:
d u 1 d u
------ = --- -------
d x l d X
With subst(l*X,x,diff(u,x)) or ratsubst(l*X,x,diff(u,x)) , I get:
d u d u
------ = ------------
d x d (l*X)
Any Ideas??? expand does not work.
I have the same problem with the function u, when I want to substitute u
with l*U. Here l is constant, U is function of x. What I want to get is:
d u d U
------ = l ---------
d x d x
With subst(l*X,x,diff(u,x)) or ratsubst(l*X,x,diff(u,x)) , I get:
d u d (l*U)
------ = ------------
d x d x
Again expand does not help.
Many thanks in advance.
Marc Hodapp