The origin of the concept of functions has always been closely linked to the study of the phenomena of change. The oldest written references can be found amongst the writings of Babylonian astronomers. In the Middle Ages the study of functions appeared to be linked to the concept of movement. Nicole Oresme (1323-1392), a scholar interested in this concept, gave graphical representations showing change in velocity with respect to time. Three centuries later, Galileo studied movement from a qua...