custom equation fit - function value and YDATA sizes are not equal

Hello,

I have data to make a fit with custom equation and would like to find the 3 parameters using lsqcurvefit

F = @(x,xdata) (x(1)+(x(2)/xdata^2))*exp(-xdata/x(3));

Here is my code:

****************

load("mydata.mat")
t = mydata(:,1);
y=mydata(:,2);
plot(t,y,'ro')
F = @(x,xdata) (x(1)+(x(2)/xdata.^2))*exp(-xdata/x(3));
x0 = [1 1 7];
[x,resnorm,~,exitflag,output] = lsqcurvefit(F,x0,t,y) 
hold on
plot(t,F(x,t))
hold off
set(gca, 'YScale', 'log')

**********************************

X(1), x(2) and x(3) are the coefficient I would like to find out. When I run I got the following error:

Function value and YDATA sizes are not equal

I searched and find an example at:

https://www.mathworks.com/matlabcentral/answers/412015-lsqcurvefit-question-function-value-and-ydata-sizes-are-not-equal

mentioning that I need to elementwise operations to declare your function.

I tried make mine as elementawise but so far it did not work. How I make my equation elamemntalwise?

Thank you

Birsen

Answer 1

[Sam Chak]

Hi Birsen

I think there should be dots here:

F = @(x,xdata) (x(1) + (x(2)./(xdata.^2))).*exp(- xdata/x(3));