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curve fitting with fminsearch

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Hello all,
I'm trying to learn MATLAB and take a course for that, and i have a homework that i can't solve. I have experimental datas for x and y variables(total 11 each) and the question asks me to fit the datas by using 'fminsearch' .
Can anyone help me how can i find the best curve and write a proper code? Thank you
x=[3, 5, 7, 10, 13, 17, 20, 23, 25, 29, 31];
y=[1.1 , 2.0 , 3.7 , 9.0 , 22.2 , 73.8 , 181.5,446.5 , 813.6 , 2701.3 , 4922.1];
  2 Comments
Burak Akayoglu
Burak Akayoglu on 18 May 2020
Well, i've tried to write those, but i know it's false.
In the question, x vs y datas are going to be fitted a curve (i think it's gonna be y= a*exp(bx) ) by using fminsearch, and find the parameters. I did it by using "cftool" but i couldnt do it with fminsearch. It would be great if you tell me how can i do that? thanks
f=@(x) a*exp(b*x);
x0=[2,1];
options = optimset('PlotFcns',@optimplotfval, 'Display','iter');
x = fminsearch(f,,x0,options)

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Accepted Answer

Ameer Hamza
Ameer Hamza on 18 May 2020
Study this example
x = [3, 5, 7, 10, 13, 17, 20, 23, 25, 29, 31];
y = [1.1 , 2.0 , 3.7 , 9.0 , 22.2 , 73.8 , 181.5,446.5 , 813.6 , 2701.3 , 4922.1];
f = @(a,b,x) a*exp(b*x);
obj_fun = @(params) norm(f(params(1), params(2), x)-y);
sol = fminsearch(obj_fun, rand(1,2));
a_sol = sol(1);
b_sol = sol(2);
figure;
plot(x, y, '+', 'MarkerSize', 10, 'LineWidth', 2)
hold on
plot(x, f(a_sol, b_sol, x), '-')
  3 Comments
Burak Akayoglu
Burak Akayoglu on 18 May 2020
Thankyou very much Ameer and John. Your answers help me a lot both solve the question and understand the concept. Thank you for your time and effort again.

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More Answers (1)

Ang Feng
Ang Feng on 18 May 2020
Hi Burak,
This link is certainly helpful
Matlab has very good documentation.
Good luck
  1 Comment
Burak Akayoglu
Burak Akayoglu on 18 May 2020
Hi Ang,
Thanks for your answer. I will check this documentation

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