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

Question

LB 2020-10-31

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/632309-fitting-model-this-expression-has-no-coefficients-or-non-scalar-coefficients

回答： Juhi Singh 2020-11-5

采纳的回答： Juhi Singh

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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

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LB 2020-11-3

@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 2020-11-4

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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

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Answer 1

Juhi Singh 2020-11-5

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/632309-fitting-model-this-expression-has-no-coefficients-or-non-scalar-coefficients#answer_534885

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