(Curve fitting) fitting a specific equation to experimental data

Dear all, I have several experimental data and I know the governing nonlinear equation of these data. Now I am trying to find constants/parameters in this equation. But there are 5 unknowns in this equation. Thanks Best regards Victor

Answer 1

[Andrei Bobrov]

try nlinfit

[Victor]

Dear Andrei,

Thanks for your comment.

May I ask you to have a look to the example in:

http://www.mathworks.co.uk/help/toolbox/stats/nlinfit.html

I can not understand the role of part 2: "Generate synthetic data with parameters a = [1;3;2]". Do you have any idea what is the concept behind it?

It is a little bit puzzling for me.

Thanks

[Andrei Bobrov]

this is eg

[Victor]

Dear Andrei,

Thanks.

May I ask you to follow this simple example. it gives me strange error!

clc

clear

%Suppose matrix of X is experimental data and is composed of x' and y' and matrix a is unknown

%parameters and the known equation is yi = a1 + a2exp(–a3xi)

mdl = @(a,X)(X(:,2)-a(1) + a(2)*exp(-a(3)*X(:,1)));

%arbitrary guess a0 = [2;2;2]:

a = [1;3;2];

x = [0,10,20];

y= [0,5,10];

X=[x',y'];

func = mdl(a,X) ;

a0 = [2;2;2];

[ahat,r,J,cov,mse] = nlinfit(x,y,mdl,a0);

ahat