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Want to make linear fitting and plot both graph on the same curve

Asked by Phong Pham on 19 Mar 2013
I have x, y data
x=[0;0.100000000000000;0.200000000000000;0.300000000000000;0.400000000000000;0.500000000000000;0.600000000000000];
y=[4.67178152947921e-06;4.67353333624452e-06;4.70560728038426e-06;4.74873086195845e-06;4.77333265701103e-06;4.84630647442201e-06;4.87015810633671e-06];
I want to plot x vs y and want to have y-axis in log scale ( NOT log the y data)
this is how I make y -axis with log scale
plot(x,y)
set(gca,'YScale','log')
hold on
Note: x data starts from 0
Now I want to fit a line and show the slope of that curve fitting line + original curve
this is for fitting line.
p=polyfit(x,(y),1);
q=polyval(p,x);
plot(x,q).
It seems to be not right because the fit line isn't straight (it likes power fit or exponential) because it does not start at Initial point . Note log scale ( not log(data))
Please helps. Thanks

  1 Comment

This is a duplicate of http://www.mathworks.com/matlabcentral/answers/67684-want-to-fit-linear-curve-on-my-data. Please do not post duplicates, it tends upsets the people who are likely to provide answers.

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1 Answer

Answer by bym
on 19 Mar 2013
 Accepted Answer

you are going to have to transform your data:
x=[0;0.100000000000000;0.200000000000000;0.300000000000000;0.400000000000000;0.500000000000000;0.600000000000000];
y=[4.67178152947921e-06;4.67353333624452e-06;4.70560728038426e-06;4.74873086195845e-06;4.77333265701103e-06;4.84630647442201e-06;4.87015810633671e-06];
semilogy(x,y,'bo')
c = polyfit(x,log(y),1)
p = polyval(c,x)
hold
semilogy(x,exp(p),'g')

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