How pca() function works in matlab

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Atinesh Singh
Atinesh Singh 2016-8-11
评论： Walter Roberson 2016-8-16
I'm trying to apply pca() function on 3d data, But I'm getting empty COEFF matrix
x1 = randn(400,1);
y1 = randn(400,1);
z1 = randn(400,1);
plot3(x1,y1,z1,'r.');
[COEFF] = pca([x1;y1;z1]')

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Jason Millen
Jason Millen 2016-8-16
编辑：Jason Millen 2016-8-16
The reason you are getting an empty 1200-by-0 matrix is because you are passing a 1-by-1200 matrix to pca.
I believe what you want to do is pass it a 400-by-3 matrix, which can be accomplished with [x1';y1';z1']'. Thus, if you call pca([x1';y1';z1']'), you will get a 3-by-3 coefficient matrix.
If you would like to read up more on the documentation for pca(), you can find it here.
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Jason Millen
Jason Millen 2016-8-16
I believe there is a transpose operator given before the matrix is passed into pca, making it 1-by-1200. Please correct me if I am wrong.
Walter Roberson
Walter Roberson 2016-8-16
Ah, you are correct, I missed that.

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