Hi All, I'm trying to find a sine function that models the cyclic and seasonal nature of retail sales across the years. I've tried several combinations including some basic attempts at complex plots of sin(x), but am now starting to wonder if there is even a simple solution to the problem. I've searched google for images of plots but maybe I'm not entering the right keywords? Anyway I'm gonna have to write out the description. The units right now don't matter since I can't even get the proper shape of the curve. I did a polynomial fit to average monthly data and got the fifth order polynomial that fits the data from x=1 to x=12 (for the months 1 to 12): y = -1.225*x^5 + 40.785*x^4 - 479.82*x^3 + 2325.3*x^2 - 4029.5*x + 1554.433 view wolframalpha plot I'm basically trying to find a sine function that repeats this basic pattern for every year since I need to then apply time-dependent attenuation and perhaps other functions to it. The closest I got was through complex plots like this: y = (sin(pi*x-pi/2)) - re(sqrt(sin(pi/2*(x+2))))^2 view wolframalpha plot Will greatly appreciate any help!