MATLAB: How to constrain the lower and upper bounds in lsqcurvefit

curve fittinglsqcurvefitMATLAB

Hi,
For a data set (x, y), I am trying to fit a function f(m, x) using lsqcurvefit. I write as follow:
x=xdata;
y=ydata;
fun=f(m,x);
m0=[m01; m02; m03]; %these are real numbers

lb=[0; 0; 0];
ub=[ub1; ub2; ub3]; %these are real numbers
m=lsqcurvefit(fun, m0, xdata, ydata, lb, ub);
However, sometimes it obeys the bounds and sometimes it does not while fitting. Could anyone please help me if there is any way of constraining the bounds?
Thank you very much in advance!
Kind regards,
Arun

Best Answer

This seems to work okay,
for i=1:2
    [xdata,is]=sort(realpart(:, i));
    ydata=imaginarypart(is, i);
    fun=@(m,xdata) ((((m(2)-m(1)).*tan(pi.*m(3)/2))/2)+((sqrt((((m(2)-m(1)).*tan(pi.*m(3)/2)).^2)-(4.*((xdata.*xdata)-(xdata.*(m(1)+m(2)))+(((m(1)+m(2)).^2)/4)-(((m(2)-m(1)).^2)/(4.*((sin(pi.*(m(3)-1)/2)).^2)))+(((m(2)-m(1)).^2).*((tan(pi.*m(3)/2)).^2)/4)))))/2));
    m0=[0.45; 0.1815; 0.0735];
    lb=[0; 0; 0];
    ub=[2, 0.75, 0.25];
    [m,resnorm,residual,exitflag,stats]=lsqcurvefit(@(m,xd) abs(fun(m,xd)), m0, xdata, ydata, lb, ub);
    plot(xdata, ydata, 'o', 'linewidth', 1.5); hold on;
    plot(xdata, fun(m, xdata), '-', 'linewidth', 1.5);
    output(i, 1:3)=m(1:3, 1);
end
output =
    0.3522    0.0000    0.1771
    0.3676    0.0239    0.1444
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