Moving objects code

Hi everybody, I am trying to find out a formula to move an object, from on point to another, in a variable speed (fast at first, slowing down at the end).
This is what I have came out with. Can anyone suggest a better way?

Thanks a lot for your help

 	this.onEnterFrame = function() {
 		my_mc._x += (desiredXcoordinate - my_mc._x) / speed;