How to plot a fitted curve?

Question

afrya 2013-12-18

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https://ww2.mathworks.cn/matlabcentral/answers/110128-how-to-plot-a-fitted-curve

评论： Wayne King 2013-12-18

Hello,

I would like to fit a curve with the following function: y=a-b*c^x

I used this expression with matlab: ft=fittype('a-b*c^x') However,I have a problem when I plot the fit.

I get this message:

Error using plot Conversion to double from fittype is not possible.

Error in project8 (line 149) plot(ft,y2,Av)

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Answer 1

Wayne King 2013-12-18

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https://ww2.mathworks.cn/matlabcentral/answers/110128-how-to-plot-a-fitted-curve#answer_118749

编辑：Wayne King 2013-12-18

在 MATLAB Online 中打开

Did you actually call fit() after you definted your fit type?

a = 2;
b = 3;
x = (0:100)';
y = 2-3*x;
ft=fittype('a+b*x') 
f = fit(x,y,ft);
plot(f)
hold on;
plot(x,y)

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afrya 2013-12-18

no, I didn't call fit after I defined fit type. Perhaphs, this is the reason of the error message from matlab. My function isn't 'a+b*x' but 'a+b*c^x'

Wayne King 2013-12-18

I was just showing you an example, not trying to do exactly what you are trying to do. I think I answered your question then, the problem is you have to use fit() to obtain the actual fit.

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