Problem fitting with lsqcurvefit

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im getting the following error while executing the code "Index exceeds the number of array elements (2)", the goal is to fit a curve to points using a certain Formula:
[name,path]=uigetfile({'*.xlsx'});
Error using matlab.internal.lang.capability.Capability.require
Support for Java user interfaces is required, which is not available on this platform.

Error in uigetfile (line 117)
Capability.require(Capability.Swing);
filename = [path name];
opts = detectImportOptions(filename);
preview(filename,opts);
newtable = readtable(filename);
x = newtable{:,1};
y = newtable{:,2};
fun = @(w,x) sqrt(w(1)^2+w(2)^2*(x-w(3))^2)
x0 = [1 1];
w = lsqcurvefit(fun,x0,x,y)

Accepted Answer

Torsten
Torsten on 12 Sep 2022
M = [26 93
27 67.9
28 54.5
29 20.5
29.1 20.6
29.2 17.6
29.3 15.7
29.4 13
29.5 12
29.6 9.2
29.7 8.7
29.8 6
29.9 5.4
30 6.3
30.1 7.2
30.2 8.3
30.3 12.3
30.4 12.4
30.5 16.4
30.6 18.3
30.7 21.5
30.8 23.7
30.9 27.6
31 28.7
31.1 32.1
31.2 34.6
31.3 36.3
31.4 39.1
31.5 40.6
31.6 44.2
31.7 48.2
31.8 50.5
31.9 53.8
32 55.9
33 77.1];
x = M(:,1);
y = M(:,2);
fun = @(w) sqrt(w(1)^2+w(2)^2*(x-w(3)).^2);
fun2 = @(w)fun(w)-y;
w0 = [1 1 1];
w = lsqnonlin(fun2,w0)
Local minimum possible. lsqnonlin stopped because the final change in the sum of squares relative to its initial value is less than the value of the function tolerance.
w = 1×3
5.7432 24.9821 29.8623
hold on
plot(x,y,'o')
plot(x,fun(w))
hold off

More Answers (1)

Matt J
Matt J on 12 Sep 2022
Edited: Matt J on 12 Sep 2022
Your model has 3 unknowns w(1), w(2), and w(3). However, you are only providing initial guesses x0 for 2 of these variables.

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