Residuals from Regress

Question

Jamie Johnston 2011-4-14

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https://ww2.mathworks.cn/matlabcentral/answers/5517-residuals-from-regress

I'm trying to get the residual error from a linear fit between two variables and the residuals I get from the regress function make no sense and don't match what I get from the data fitting gui (which looks correct). What is the difference in the procedures here and how can I programmatically get the residuals I see through the data fitting menu option?

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the cyclist 2011-4-14

Can post the code that uses the regress function and seems suspicious to you?

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Answer 1

Richard Willey 2011-4-14

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https://ww2.mathworks.cn/matlabcentral/answers/5517-residuals-from-regress#answer_7732

在 MATLAB Online 中打开

% Generate some random data
X = linspace(1,100,100)';
Y = X + randn(100,1);
% Use Curve Fitting Toolbox to generate a fit
% In your workflow, you'd create the fit in cftool and then export the
% model to MATLAB as a fit object
foo = fit(X,Y,'poly1')
% Calculate residuals
resid1 = Y - foo(X)
% Use regress to compute residuals
b = regress(Y, [ones(length(X),1) X])
Yhat = [ones(length(X),1) X]*b;
resid2 = Y - Yhat
% Check that the residuals are the same
resid1./resid2

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Jamie Johnston 2011-4-14

Thanks Richard - I was simply missing the second column for the X variable...looks to be working now.

Richard Willey 2011-4-14

Easy mistake to make. regress gives you really fine grained control over your design matrix. However, in turn you need to do things like add a ones vector for your constant and the like...

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