I'm trying to draw the function Fz4=f(fx4) which has a circular shape but curve fitting won't work (it only plots lines or strange shapes). The goal is to get something that looks like the following figure.
(you can find the picture here: http://www.tpe-avion.fr/sites/default/files/u1/33_2.jpg)
I've tried using the lsqnonlin function (because, well, why not). I've also tried plotting it in polar coordinates but nothing will work.