domo:
I have a model in Simulink....
Use the visualization in Matlab/Simulink. Add plots in your Matlab model that connects to Arduino. You are not really using the Arduino library with using the Matlab/Simulink target for Arduino. Instead a small "server" is uploaded which your model in Matlab/Simulink may "talk" to and get values from the different Arduino hardware resources; e.g. digital and analog pin, etc.
http://www.mathworks.se/help/simulink/arduino.html
For more details I would recommend asking in a forum for Matlab/Simulink.
Cheers!