# Using the \ operator to fit a parabolic curve to a data set.

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Petch Anuwutthinawin on 20 Jul 2021
Commented: John D'Errico on 20 Jul 2021
%for a certain file, the first column is the independent variable and
%second is the dependent variable.
h=C([2:13],1);
x=[h ones(length(h),1)] %I use a column of ones in order to simulate a constant secondary dependent variable.
y=C([2:13],2); % the dependent variable
V=x\y %This command only gives me one value, that is just a linear fit. How do I make this use a parabolic fit instead?

Torsten on 20 Jul 2021
Replace x by
x = [h.^2 h ones(length(h),1)]
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John D'Errico on 20 Jul 2021
@Tesfaye Girma - NO. Don't tell people to use an inferior method to estimate a linear regression model.
In MATLAB, it is correct to use this:
coef = M\x;
Use of the normal equations (what you showed) will cause significantly increased sensitivity to poorly conditioned problems. That scheme will completely fail to work on many solvable problems.

### More Answers (1)

Simon Chan on 20 Jul 2021