Differentiate a function by a function

Question

I'm just a little bit lost here. I'm using the latest MATLAB release with the symbolic maths toolbox. At the moment I'm working on a system, which has equations like x=theta(t)+2 (of course a lot more complicated and longer). Now I would like to differentiate this equation by theta(t). Hence, I should get x=1. However, if I use the diff(x,theta) command I only get the message Invalid variable.

How do I do it? What am I doing wrong?

Thanks!

Answer 1

I used to have the same problem, but using Maple or sympy. Try substituting theta(t) by theta in the right hand side of the equation and then differentiate wrt. theta.