I am trying to do a nonlinear fit of the attached data, which is the blue decaying sine or cosine wave in the attached image.
I want to fit the data into the function of a*exp((q1+i*q2)*x)/sqrt(x), where a, q1 and q2 are real numbers.
I have tried to use lsqnonlin, but could not limit those three fitting variables to be real. And the fitted results do not make sense.
Any help will be much appreciated.