Fitting data with custom equation
显示 更早的评论
Hi,
I have some datas to fit with by the following equation : d*atan(b*(x+a))+c . I've done it by the " curve fitting tool" how I can incorporate this process in a matlab script ? I'd like to obtain the parameter a,b,c,d as an answer.
Thanks.
采纳的回答
Hi,
you can use this code:
% Some data - replace it with yours (its from an earlier project)
x = [177600,961200, 2504000, 4997000, 8884000]';
y = [6.754, 24.416, 58.622, 107.980, 154.507]';
% Define Start points, fit-function and fit curve
x0 = [1 1 1 1];
fitfun = fittype( @(a,b,c,d,x) d*atan(b*(x+a))+c );
[fitted_curve,gof] = fit(x,y,fitfun,'StartPoint',x0)
% Save the coeffiecient values for a,b,c and d in a vector
coeffvals = coeffvalues(fitted_curve);
% Plot results
scatter(x, y, 'r+')
hold on
plot(x,fitted_curve(x))
hold off
Due to, that this code is taken from an older project and the values dont represent your function the result here is a very bad fit - but to show how it works with a custom function inside a script it should be good enough.
Best regards
Stephan
5 个评论
Priodyuti Pradhan
2020-4-6
Thanks a lot for sharing! Really helpful!
sandeep
2022-8-3
Is there a way to find the appropriate intial guess?
Rekib Uddin
2023-8-19
Dear all,
How can we consider conditions in the custom equation....
e.g. y=-0.18 at x=0
Thanks and Regards
You can insert the point in the custom equation thereby reducing the number of unknown parameters:
d*atan(b*(0+a)) + c = -0.18
-> d*atan(b*a) + c = -0.18
-> c = -0.18 - d*atan(b*a)
Thus the modified custom equation to be fitted reads:
d*(atan(b*(x+a)) - atan(b*a)) - 0.18
which now has only 3 instead of 4 unknown parameters.
Zeyu Ma
2023-8-31
Hi there, I wonder how to restrict the values of the parameters.
For example, force parameter a to be 0<a<1.
Thank you!
更多回答（1 个）
Valrhona
2020-9-28
0 个投票
I have a question regarding the curve fitting tool itself.
How can I change the z=f(x,y) to f(x).
I cannot change the x, y, or z data in this curve fitting tool.
I would like to use a custom f(x) function (not f(x,y))
Many thanks!
2 个评论
Koral Villalobos
2021-4-27
I need help with this too
sandeep
2022-8-3
is there a way to find the appropriate intial guess?
类别
在 帮助中心 和 File Exchange 中查找有关 Get Started with Curve Fitting Toolbox 的更多信息
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!
Translated by 
