Fitting Model : This expression has no coefficients or non-scalar coefficients

Hi,

Im trying to fit a model i've made to some experimental data, however I'm getting an error i don't seem to understand.

I followed the fittype guide.

Heres my code:

%This is the model
function pdf = pdf_GG(Var)
I=0.3;
LKK = sqrt(Var);

alpha = (exp((5.19.*LKK.^2)./((1 + 9.01.*LKK.^(12/5)).^(7/6))) -1).^-1;
beta  = (exp((6.22.*LKK.^2)./((1 + 22.39.*LKK.^(12/5)).^(5/6))) -1).^-1;


k = (alpha+beta)./2;
k1 = alpha.*beta;
H =4.*(k1.^k)./(gamma(alpha).*gamma(beta));
H1 = I.^(k-1);
D = 6.*sqrt(k1.*I);
pdf = H.*H1.*besselk((alpha-beta),D);

And now my main code:

%Fitting
x0=[0.2];
fitfun=fittype(@(Var) pdf_GG( Var),'independent','Var');% this is where i get the this expression has no coeffiecients or non-scalar coefficients error
[fitted_curve,gof]=fit(ctrs',pn',fitfun,'StartPoint',x0);

Any help on how i should proceed to make this fit?Thank you very much

[Sindar]

Maybe save it as a file and use this syntax:

fitfun = fittype( 'pdf_GG(Var)' )

[LB]

@Sindar I tried but that just replies with an error: "Custom equations must produce an output vector, matrix or array that is the same size and shape as the input data.This custom equation fails to meet that requirement" How can i fix this?The equation is suposed to return PDF values

[Sindar]

Does this return a 2-element array? (and do you expect it to?)

pdf_GG([0 1])

If not, add a breakpoint at the last line and check the sizes of all the intermediate variables

Answer 1

[Juhi Singh]

The error is being encountered because pdf_GG() returns a vector. Unfortunately, specifying the coefficients as vector is not supported. There is no workaround.