Error in matlab code for best c and gamma using svmtrain()

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Astha Ameta 2017-1-20

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https://ww2.mathworks.cn/matlabcentral/answers/321202-error-in-matlab-code-for-best-c-and-gamma-using-svmtrain

评论： Walter Roberson 2017-1-21

In the following code snippet:

for i=1:numel(C)

cv_acc(i) = svmtrain(labels, data, sprintf('-c %f -g %f -v %d ', 2^C(i), 2^gamma(i), folds));

end

I get the Error: label vector and instance matrix must be double In an assignment A(I) = B, the number of elements in B and I must be the same.

Please advise.

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Answer 1

Walter Roberson 2017-1-20

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It looks to me that you are using libsvm syntax. However I suspect that you are getting the svmtrain that is part of the Statistics toolbox which uses a different syntax.

Your code assumes that you will get back a single value each time. We cannot tell whether it expecting a numeric value or a structure member or a cell array. Whatever it expected, it is not getting back exactly one of whatever is being returned. That can happen if a routine returns an empty variable rather than a single value.

If you were expecting a single numeric value returned then you are probably not calling the routine correctly.

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Astha Ameta 2017-1-21

The same statement has been used by many programmers through libsvm, so I am unable to understand what is going wrong here.

What should be the correct way to call the routine as I need to return the value of svmtrain in an array variable only so that I can find the maximum of it by comparing.