This question already has an answer here:

Let's say that I have some symbolic expression of a function $x(t)$, and would like to obtain its derivative $x'(t)$.

However, I also have the following two identities, $\xi = \omega t$, and $\eta = \epsilon t$.

Is there any way to have Mathematica symbolically express $x'(t)$ in terms of partials of $\xi$ and $\eta$?

I've already attempted the method recommended by Alex in a related question here, but it doesn't seem to work for this situation. Ideally, the method would preserve the structure of the equations so that one could use DSolve or other standard symbolic manipulations on them.


marked as duplicate by xzczd differential-equations Feb 17 at 4:34

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.


You should look at DChange

DChange[D[X[t], {t, 1}], eta == w*t, t, eta, X[t]]

w X'[eta]

Note: For change of variable, there should be one to one correspondence. So, it seems impossible to change $t$ to $\eta$ and $\xi$ at the same time. Correct me if I am wrong.


Not the answer you're looking for? Browse other questions tagged or ask your own question.