minimize error b/w reference inputs and measured outputs using least squares

Hi, I'm working on a MIMO system. It has 4 inputs and 3 outputs. I need system's outputs to track input reference trajectories. One logical way could be to minimize error b/w reference inputs and measured outputs using least squares. But, I don't know how to do all this... I need quick help on this. Trajectories to be followed are: http://i46.tinypic.com/25g5s41.jpg and the natural response of the system is: http://i50.tinypic.com/vfdu3d.jpg... Anticipating a quick response!