Nlinfit

Im trying to fit a non linear curve as below;

x=areas40{1}(3,:); >> [a,b]=hist(x,30); >> mdl=@(a,b,x)(-a*exp.^-b); >> mdl=@(c,d,x)(-c*exp.^-d); >> b0=1; >> nlintool(a,b,mdl,b0); ??? Error using ==> nlinfit at 120 Error evaluating model function '@(c,d,x)(-c*exp.^-d)'.

Error in ==> nlintool at 193 [ud.beta, residuals, J] = nlinfit(x,y,model,beta0);

Caused by: Error using ==> exp Not enough input arguments.

and im struggling to understand why an help would be appreciated

thanks

Answer 1

[the cyclist]

Since I don't know what "areas" is, it is not possible for me to try to run your code.

However, I notice that you wrote, for example,

 >> exp.^-b

That is not correct MATLAB syntax. exp() is a function that requires an argument; it is not the value "e". So, I am guessing you meant maybe

 >> exp(-b*x)

but I am not quite sure.

ADDED LATER:

Here is a snippet of code in which I took your attempt, and changed several things to make it function.

• I put in some random exponential data
• I reordered your a and b variables as input, because I think you had them switched
• I put the fitting parameters into one vector

So, this works, but you definitely need to see if it is close to what you want to do.

x = exprnd(1,[100000 1]);

[a,b]=hist(x,30);

mdl=@(ab,x)(ab(1)*exp(-x*ab(2)));

ab0=[1;0];

nlintool(b,a,mdl,ab0)

[Matt]

Basically I am looking at the distribution of Facet areas over a crumpled piece of paper and i get an almost exponential distribution it might be a stretched exponential as above or something similar but basically im struggling to plot a non linear curve to it :/