Data Curve Fitting Not Fitting Third Point?

2019 2 20
1 个回答
更新时间：2019 2 20
2 次查看（30 天）

0 个投票

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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回答（1 个）

Kelly McGuire
Kelly McGuire 2019-2-20

0 个投票

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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