Clear Filters
Clear Filters

Function with multiple input parameters to be determined through fitting

3 views (last 30 days)
Hi, I have a function to be fitted to some experimental data, but this function has multiple fitting parameters (6 parameters). I know that one of the ways to find these fitting parameters is to pass the function, the inital guess to the parameters and the lower and upper bounds into the lsqcurvefit function.
I have already created the function, but it seems like the software doesn't know that the p(1),p(2), p(3)... are parameters. Sorry if the function is very long.
What I wanted was p to be a vector with 6 elements p(1) p(2) p(3) p(4) p(5) p(6) but it seems like the software cant differentiate betwen p and p(1) p(2) p(3) p(4) p(5) p(6). When I try running the code, the error message I got was "Not enough input arguments"
Thank you for helping
function F = EM_SS(p, E_p)
F = p(1)*(2*pi*sqrt(p(4))/E_p)*(1/p(6))*(int(sech(((E_p - E)./p(6)))*(1 + 10*p(5)*(E - p(3)) + 126*p(5)^2*(E - p(3))^2)/(1 - exp(-2*pi*sqrt(p(4)/(E - p(3))))), E, p(3), Inf, 'ArrayValued', 1)) + p(2)*(2*pi*p(4)^3/2)*1/p(6)*((1/1^3)*sech((E_p - p(3) + p(4)/1^2)./p(6)) + (1/2^3)*sech((E_p - p(3) + p(4)/2^2)./p(6)) + (1/3^3)*sech((E_p - p(3) + p(4)/3^2)./p(6)) + (1/4^3)*sech((E_p - p(3) + p(4)/4^2)./p(6)) + (1/5^3)*sech((E_p - p(3) + p(4)/5^2)./p(6)) + (1/6^3)*sech((E_p - p(3) + p(4)/6^2)./p(6)) + (1/7^3)*sech((E_p - p(3) + p(4)/7^2)./p(6)));
end
  1 Comment
Jack
Jack on 7 Jun 2024
please refer to this picture for the function to be fitted. everything other than and π is a fitting parameter. is given by: where R is also a fitting parameter. There should be a total pf 6 fitting parameters.

Sign in to comment.

Accepted Answer

Torsten
Torsten on 7 Jun 2024
Edited: Torsten on 8 Jun 2024
You have to use "integral" instead of "int" and loop over the elements in E_p:
EM_SS([1 1 1 1 1 1],1)
ans = 3.2940e+03
function F = EM_SS(p, e_p)
for i = 1:numel(e_p)
E_p = e_p(i);
F(i) = p(1)*(2*pi*sqrt(p(4))/E_p)*(1/p(6))*...
(integral(@(E)sech(((E_p - E)./p(6)))*(1 + 10*p(5)*(E - p(3)) + ...
126*p(5)^2*(E - p(3))^2)/(1 - exp(-2*pi*sqrt(p(4)/(E - p(3))))), p(3), Inf, 'ArrayValued', 1)) + ...
p(2)*(2*pi*p(4)^3/2)*1/p(6)*(...
(1/1^3)*sech((E_p - p(3) + p(4)/1^2)./p(6)) + ...
(1/2^3)*sech((E_p - p(3) + p(4)/2^2)./p(6)) + ...
(1/3^3)*sech((E_p - p(3) + p(4)/3^2)./p(6)) + ...
(1/4^3)*sech((E_p - p(3) + p(4)/4^2)./p(6)) + ...
(1/5^3)*sech((E_p - p(3) + p(4)/5^2)./p(6)) + ...
(1/6^3)*sech((E_p - p(3) + p(4)/6^2)./p(6)) + ...
(1/7^3)*sech((E_p - p(3) + p(4)/7^2)./p(6)));
end
end
  15 Comments
Torsten
Torsten on 8 Jun 2024
I think the problems will be too problem-specific to find general ressources. As said: less parameters and good initial guesses for them would be helpful. Did you plot Abs against E_p for the initial guesses you provided to get an impression of the "initial fitting quality" ?
Jack
Jack on 8 Jun 2024
I have tried doing the scatter plot of Abs against E_p but I have been trying for days to plot the curve that will fit the scatter plot.

Sign in to comment.

More Answers (0)

Categories

Find more on MATLAB in Help Center and File Exchange

Products


Release

R2024a

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!