I need a basic math formula with the following properties: * limit y between -1 and 3. * (x, y) hits (-1, 0), (0, 1) and (1, 2). * Each y value occurs only once. I managed to do this with y=4/pi*ArcTan(x)+1. But I'd like to do this without trig. I got close with y=x*2/SQRT(1+x^2)+1. But it's not right. I keep thinking it's something simple and obvious. Can you help me? NOTE: This is not homework. I'm graphing and analyzing some proportion data in excel for myself.