Finding harmonic amplitudes of a sine wave

I have got a sine wave as below, where I want to extract the amplitude of different harmonics from a data vector in matlab. can someone help me how to do it (other than fft maybe)?

[Xavier]

Why do you not want to use fft?

[Syed AWM]

because the summation of amplitudes of harmonics using fft does not equal to the max amplitude of the actual sine signal.

[Asad (Mehrzad) Khoddam]

Do you want to fit the data into a sine wave (single harmonic) ?

[Syed AWM]

no, I just need the amplitude of different harmonics

Answer 1

[Image Analyst]

Looks like that is a pure sine wave with no harmonics. How did you generate it? Why do you think there are any harmonics? None are visible to me. Do the higher harmonics just have super small power - too small to be seen at the scale of the graph you have drawn?

Anyway, I'd try using findpeaks() if you want to do it in the time/spatial domain instead of using fft() or pwelch() to do it in the frequency domain.

[Image Analyst]

Syed, I assume you've had time by now to try this, but you forgot to get back to us. Did it work?