Fitting data in x,y to a known function
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Raúl Alonso Merino
le 12 Déc 2019
Commenté : Star Strider
le 13 Déc 2019
Hi everyone. I have a function that is f = 1/(a+b*x) where a and b are the values to obtain and I have some data:
x1 = linspace(1,32,32);
y1 = [0.01 0.02 0.02 0.02 0.02 0.02 0.03 0.03 0.03 0.04 0.04 0.05 0.05 0.06 0.07 0.07 0.08 0.10 0.11 0.14 0.14 0.17 0.17 0.16 0.21 0.31 0.31 2.43 2.43 29.53 29.53 29.53];
I need to fit these two variables x1 and y1 into the function above to obtain a and b. How can I do this?
I'm sorry I'm pretty new in Matlab. Thank you.
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Star Strider
le 12 Déc 2019
x1 = linspace(1,32,32);
y1 = [0.01 0.02 0.02 0.02 0.02 0.02 0.03 0.03 0.03 0.04 0.04 0.05 0.05 0.06 0.07 0.07 0.08 0.10 0.11 0.14 0.14 0.17 0.17 0.16 0.21 0.31 0.31 2.43 2.43 29.53 29.53 29.53];
f = @(p,x) 1./(p(1) + p(2).*x);
P = fminsearch(@(p) norm(y1 - f(p,x1)), rand(2,1));
x1v = linspace(min(x1), max(x1));
figure
plot(x1, y1, 'p')
hold on
plot(x1v, f(P,x1v), '-r')
hold off
grid
producing:
P =
0.845464263829100
-0.025490734971736
where ‘P(1)=a’, and ‘P(2)=b’.
The plot appears correct, even though it looks a bit strange.
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Nicolas B.
le 12 Déc 2019
If you have it, I would recommend to use the Curve Fitting Toolbox. You can give it the expected function and it fits the parameters.
Otherwise, the only solution would be to yourself try to fit the function on the samples based on an optimization method but that requires to investigate mathematic fitting.
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