MATLAB: System of Equations with LSQCURVEFIT

data fittinglsqcurvefitsystem of equations

I would like to fit my data to a system of equations. I keep getting an error of "LSQCURVEFIT requires all values returned by user functions to be of data type double."
Any suggestions in getting my code to run correctly?
kappa1 = @(x, xdata)x(1)*xdata*x(2); % Equation 1
kappa2 = @(x, xdata)2*sqrt(2)*x(1).^2*x(2)*(-2*x(3).*(xdata+(xdata+x(3)).*log10(x(3)./...
    (xdata+x(3))))); % Equation 2
E1 = char(kappa1) % Equation listing turn to character string; then combine
E2 = char(kappa2)
ES = (['{' E1 '; ' E2 '}'])
ESF = inline(ES)
k_2 = fcum(1:2,1:2); % ydata 2 by 2 matrix, two answers for each equation for two xdata points
T = AllDataTime; % two data time points
x0 = [.618 .088 .2]; % Initial guess values
[x, resnorm] = lsqcurvefit(ESF, x0, T, k_2)

Best Answer

lsqcurvefit cannot be used to fit to a system of equations. The output of the objective function must be the same size as the ydata, and cannot be a cell array.
The original poster also had difficulty with handling symbolic functions, but there is no point in posting a solution to that part as the overall goal cannot be met using lsqcurvefit
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