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

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Petch Anuwutthinawin
Petch Anuwutthinawin le 20 Juil 2021
Commenté : John D'Errico le 20 Juil 2021
%for a certain file, the first column is the independent variable and
%second is the dependent variable.
C=xlsread('super.xlsx');
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?

Réponse acceptée

Torsten
Torsten le 20 Juil 2021
Replace x by
x = [h.^2 h ones(length(h),1)]
  2 commentaires
Tesfaye Girma
Tesfaye Girma le 20 Juil 2021
yhat = (M'*M)\(M'*x);
John D'Errico
John D'Errico le 20 Juil 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.

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Simon Chan
Simon Chan le 20 Juil 2021

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