Error with nlinfit and it said Index exceeds the number of array elements (1)

I just start learing how to use Matlab, and I was trying to run the nlinfit like this:

ogfun = @(var,x) 1./(1+exp(-(var(1)+var(2)*x)));

var=[1;1]; x=(-10:1:10);

y=logfun(var,x);

plot(x,y);

K>> beta=nlinfit(x,y,logfun,1)

Then it gave me an error said "Error using nlinfit (line 213)

Error evaluating model function '@(var,x)1./(1+exp(-(var(1)+var(2)*x)))'.

Caused by:

Index exceeds the number of array elements (1)."

I know it's a silly question but can anyone tell me why it said that index exceeds the number of array elements and what (1) stands for?

Answer 1

[Rajanya]

Hi @Aaron Lee,

I have been able to reproduce the issue at my end and the error is because the function ‘nlinfit’ demands its ‘beta0’ argument (initial parameter values) to be a vector. Here, 1 is being passed which is interpreted as a scalar. Consequently, when the ‘logfun’ function is evaluated, attempting to access ‘var(2)’ results in this error.

Modifying the ‘nlinfit’ call as shown below resolves the error.

beta = nlinfit(x,y,logfun,[1 1])

To know more about ‘nlinfit’ and its usages, you can refer to the documentation page by executing the following command from the MATLAB Command Window:

doc nlinfit

Hope this helps!