The user-func (user function) is a powerful tool that applies a lambda function to each OMChroma class. In many cases you could obtain the same result using the classes and functions of OM, but the user-function allows a higher level of abstraction and a more efficient programming.
We assume you have a good knowledge of the class-array, that is a bidimensional data structure matrix like the OMChroma classes.
For more details on class-array see the OM Documentation at http://support.ircam.fr/docs/om/om6-manual/co/ClassArray.html