Meaning of message "Expecting expand_derivatives to have been applied"

Question

Hello

I get this message in my python code solving a nonlinear problem

Expecting expand_derivatives to have been applied

Can you tell what this means. The code is rather big and I do not know which part of it gives rise to this message.

The code runs and seems to give correct solution. But I would still like to know what this message means, and whether I should try to fix it.

Comments

It is essentially impossible to answer your question without a piece of code reproducing it.