MATLAB: Sine curve fit to data with an unknown dc offset

Question

Hi. Apologies if this has been answered before, but I'd like to know if there's any way of fitting a sine curve to a sinusoidal function with unknown frequency and unknown DC offset? The function I'm trying to fit to is a standing wave and is most likely sinusoidal, but is less than half a period long.

Thanks in advance for the help.

Answer 1

Of course it is possible. Use the curve fitting toolbox.

ft = fittype('a + b*sin((x - c)/d)','indep','x');
mdl = fit(X(:),Y(:),ft,'startpoint',[1, 0.001, 1200, 1000])

I just picked off some very rough starting values from the plot.

Here, a is the DC offset. b is the amplitude of the wave, c is the shift in X, d/(2*pi) is the length of the period. You can transform that to give you frequency.