How to use harmonic fitting method

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TTA
TTA 2023-9-20
评论： TTA 2023-9-20
Hi,
Please, how can I use Harmonic fiting for the attached data to get a smooth fit.
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TTA
TTA 2023-9-20
yes but I want use harmonics to fit it to something like the attached figure
Torsten
Torsten 2023-9-20
Tell us precisely what you define as your approximating "harmonic".

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Sam Chak
Sam Chak 2023-9-20
Ran in:
Hi @TTA,
I'm interpreting your 'Harmonic' model as the 'Sum of Sine' model. If this is not the case, then you will need to create a custom nonlinear model that suits the name "Harmonic" using the fittype() function.
y = load('darta1.txt');
x = linspace(10, 60, numel(y));
[f, gof] = fit(x', y, 'sin3')
f =
General model Sin3: f(x) = a1*sin(b1*x+c1) + a2*sin(b2*x+c2) + a3*sin(b3*x+c3) Coefficients (with 95% confidence bounds): a1 = 1564 (-8.752e+04, 9.065e+04) b1 = 0.04957 (-0.1147, 0.2138) c1 = 0.1819 (-4.047, 4.411) a2 = 1363 (-8.772e+04, 9.045e+04) b2 = 0.05511 (-0.1195, 0.2297) c2 = 3.18 (-1.365, 7.725) a3 = 2.975 (2.774, 3.176) b3 = 0.3159 (0.307, 0.3248) c3 = -4.138 (-4.419, -3.857)
gof = struct with fields:
sse: 465.0567 rsquare: 0.9983 dfe: 492 adjrsquare: 0.9983 rmse: 0.9722
plot(f, x, y), grid on,
legend('data', 'Sum of Sine (type-3)', 'location', 'best')

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