Is there any way I can substitute a combination of variables.
I know this is a long short but I was wondering whether it is possible to substitute a combination of variables by something else. Let me explain it with an example.
Let f(x,y,z)=f(x)√x2+y2+z2+f(y)√x2+y2+z2+f(z)√x2+y2+z2
As we can see the combination √x2+y2+z2 occurs very often. Is there a way I call this combination some other variable, say, w. I cannot use substitute in this case as I want to leave x,y and z alone if they dont come in this specific combination √x2+y2+z2. If it were a string I could have used find and replace. But I want to use the expression as a input later on in the notebook.
Edit: I came across a sympy command which is very close to what I want to do but not quite. There is a command cse in the module simplify. However, it identifies the subexpresssion by itself. As far as I could see it does not offer the flexibility for the users to identify the subexpression. Also for some reason sage expressions cannot be converted to sympy using f._sympy_()
if there are "i"'s in the expression.
Thanks in advance.