My data describes a pseudo-periodical behaviour: the amplitude seems stable, but the frequence decreases with X, making the pseudo-period increasing exponentially. What I mean by that is that I measured that for any X I could expect a full pseudo-period to occur within the interval [X, X+exp(aX+b)], where a=7.27e-07 and b=10.12
I would like to approximate this with a pseudo-sinusoid (a function like F:X->C*sin(g(X)) where g is monotonous).
I know that I would need g(X+exp(aX+b)) = g(X)+2*Pi, but I am stuck there.
My goal is then to do something like a Fourier transform (not really, of course, since the function is not truly periodic, but you should get the idea), and see if it gets interesting.