MATLAB: Does anybody have expertise with matlab SVM classifier

Bioinformatics Toolboxfuzzymachine learningsvm classification

Does anybody know if it's possible to extract more information from SVM classify than just the group? I'm hoping I'll be able to determine the distance from the class boundary. It can serve as a measure of confidence in the classification, or a fuzziness to the membership definition. It seems like that should be possible, I'm wondering if matlab has already implemented that functionality. If not, can anybody suggest a way to implement this as an accessory function to matlab's svm classification?

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See my comments at the bottom of this thread http://www.mathworks.com/matlabcentral/answers/62757-how-do-i-find-slack-variables-in-svm-distance-to-the-boundary

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MATLAB: How to do a ROC analysis using Matlab build-in SVM (Not LibSVM)

Well, there is an answer here http://www.mathworks.com/matlabcentral/answers/64475-does-anybody-have-expertise-with-matlab-svm-classifier, with a reference to another thread. I am collecting all the pieces in one place.

Assume your class labels are -1 and +1, assume that you have trained with 'autoscale' set to true by default, let svm be the struct for the trained SVM model, and let Xnew be the new data for which you need to compute the soft scores.

shift = svm.ScaleData.shift;
scale = svm.ScaleData.scaleFactor;
Xnew = bsxfun(@plus,Xnew,shift);
Xnew = bsxfun(@times,Xnew,scale);
sv = svm.SupportVectors;
alphaHat = svm.Alpha;
bias = svm.Bias;
kfun = svm.KernelFunction;
kfunargs = svm.KernelFunctionArgs;
f = kfun(sv,Xnew,kfunargs{:})'*alphaHat(:) + bias;
f = -f; % flip the sign to get the score for the +1 class

Then call perfcurve(true_labels,f,1).

MATLAB: ROC curve with Matlab using svmtrain

The error says that 1 is not found in t2. Note that your groups variable is logical, and so are t1 and t2, but 1 is double. Try replacing 1 with true or replacing t2 with double(t2).

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Related Solutions

MATLAB: How to do a ROC analysis using Matlab build-in SVM (Not LibSVM)

MATLAB: ROC curve with Matlab using svmtrain

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