Van der Pol equation : The mathematical model for the system is a well known second order ordinary differential equation with cubic nonlinearity. You'll find this model used in many examples in MathWorks Documentation.
Also, to open the VDP-Simulink, run the below command by entering it in the MATLAB Command Window.
Note : Web browsers do not support MATLAB commands.
You can use 'vdp' as variable name because this is a model name, and not any function name.