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Data Curve Fitting Not Fitting Third Point?

Asked by Kelly McGuire on 20 Feb 2019
Latest activity Answered by Kelly McGuire on 20 Feb 2019
Any ideas why it appears the third data point is not being fit?
xdata = [1;10;100];
ydata = [0;0;0.3];
fun = @(x,xdata)(1./(1+(x(1)./xdata).^x(2)));
lb = [1,1];
ub = [1000,5];
x0 = [50,2];
x = lsqcurvefit(fun,x0,xdata,ydata,lb,ub)
figure
hold on
plot(xdata,ydata,'ko');
xlim([0 200]);
xlabel('Concentration','FontWeight','bold');
ylim([0 1]);
ylabel('Average Mortality','FontWeight','bold');
box off
y = 0:200;
plot(1./(1+(x(1)./y)).^x(2))
xlim([0 200])
ylim([0 1])

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1 Answer

Answer by Kelly McGuire on 20 Feb 2019

Fixed the problem. In the second plot, my x(2) was in the wrong term. It should have been brought into the left parthensis. Here is the correct code:
xdata = [1;10;100];
ydata = [0;0;0.3];
fun = @(x,xdata)(1./(1+(x(1)./xdata).^x(2)));
lb = [170,1];
ub = [200,2];
x0 = [180,1.6];
%x = lsqcurvefit(fun,x0,xdata,ydata,lb,ub)
opts = optimset('MaxFunEvals',1E+4, 'MaxIter',1E+4 );
x = fminsearch(@(x) norm(ydata - fun(x,xdata)), x0, opts)
figure
hold on
plot(xdata,ydata,'ko');
xlim([0 200]);
xlabel('Concentration','FontWeight','bold');
ylim([0 1]);
ylabel('Average Mortality','FontWeight','bold');
box off
y = 0:600;
plot(1./(1+(x(1)./y).^x(2)))
xlim([0 200])
ylim([0 1])

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