STEPPER MOTOR EQUATIONS

I am making a comparison between the perfomance of servo motors and stepper motors from the point of view of the presicion position control.
I could make step response analysis of the dc servo motor using PID controller , but i don't know how to model a stepper motor nor how to make a simulation for it .
i am using the MATLAB program , my concern is about high inertial loads.
please help me for supplying me the stepper motor( HYBRID- VARIABLE RELUCTANCE - PERMENANT MAGNET )equations or the way to model or simulate it.

 RE: STEPPER MOTOR EQUATIONS

Check for data sheets for specific stepper motors. They have a lot of information. Also check for data sheets for controller chips. Some of them has a full "howto" section about dimensioning etc for different types of motors.