Auxiliary variable function not defined.

The error message "Auxiliary variable function not defined" suggests that there is an undefined function that is being used in your code.

To resolve this issue, you need to make sure that all the functions you are using in your code are properly defined. Check if you have misspelled the function name or if there is a typo in the function definition.

If you are using a third-party library, make sure that you have imported it correctly and that all the dependencies are installed.

It would be helpful to see a code snippet or more information about the context of the error to provide a more specific solution.