Hello everyone: I have some question using the FFT in matlab for data interpolating. I don't know what the relation between the normal fourier series and the real, image number. For example, given a set of measurement data, I can use the curve fitting toolbox to fit a curve. The general equation is f(x) = a0 + a1*cos(x*w) + b1*sin(x*w) + a2*cos(2*x*w) + b2*sin(2*x*w) for a a factor 2 fourier series. The a0,a1,b1,a2,b2 and w can be obtained. When I use the FFT function, it returns the Fourier transform of each column of the matrix. This matrix has real and imaginary part. Are their any relationship between those two results ? if yes, what should I do to convert the FFT results into a normal fourier series format? Thank in advance.