gluperPECTIVE

Hey, Can neone tell me what is the exact matrix operation applied by gluPerspective(fovy,aspect,near,far) I do have some idea but i am not sure how to do the same thing which this command does. I need to know the exact details so that i can write my own function which does the same thing.(just for learning!!) Thanx On course to my first FPS engine , zoooooom