MATLAB: Algebraic Problem in writing the function for LSQNONLIN tool in the Optimization Toolbox

4d fittinglsqnonlinMATLABnonlinearOptimization Toolbox

Hello,
I am using lsqnonlin for fitting a non linear equation to the model
z=Ax+(B*log(y))+(C/y)+(D*x*log(1+y))
X matrix is 10×2 double matrix. 1st column contains values for x and 2nd column contains values for y.
x(1) and x(2) represent x and y respectively in the model.
The function definition to be used in lsqnonlin is as follows:
function F=myfun(x,X,Z) k=1:10; F=(x(1)*X(k,1))+(x(2)*log(X(k,2)))+(x(3)/X(k,2))+(x(4)*X(k,1)*log(1+X(k,2)))-Z(k); end
I have all the values for the X and the Z matrix.
The problem is that whenever I am trying to call the myfun function, the error which it shows is:
??? Error using ==> plus Matrix dimensions must agree.
Error in ==> myfun at 3 F=( x(1) * X(k,1) )+( x(2) * log(X(k,2) )+( x(3) / X(k,2) )+( x(4) * X(k,1) * log(1+X(k,2) ) ) – Z(k);
Please clear this up.
Thank you.

Best Answer

use function lsqcurvefit
eg:
A = .5;
B = 4.1;
C = .6;
D = .6;
x = (.01:.01:1)';y = (.01:.01:1)';
z = A*x+(B*log(y))+(C./y)+(D*x.*log(1+y))+.1*rand(size(x));
%solution:
f = @(a,X) a(1) * X(:,1) + a(2) * log(X(:,2)) +  a(3) ./ X(:,2) + a(4) * X(:,1) .* log(1+X(:,2) );
abcd = lsqcurvefit(f,[0 0 0 0],[x y],z)
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