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Problem with PCA::read

I ran into a problem with the PCA::read() function. Saving a PCA object with PCA::write went well (I used XML format), but reading the file didn't go well:

First, there is no documentation* on this. I didn't find anything in the examples, neither.
The read/write is inconsistent. read() should also accept FileStorage as parameter.
Using
```
FileStorage fs("pcafile.xml");
pca.read(fs["PCA"]);
```
gives (!fs.empty()) exception (even if this is the node it needs).

copying directly the source of the read function:

read(fs["vectors"], pca.eigenvectors);
read(fs["values"], pca.eigenvalues);
read(fs["mean"], pca.mean);

reads correctly the object.

Am I doing something wrong? Anyway, I think this should be corrected in the source code.

*BTW, the documentation of OpenCV 3.x seems much worse than OpenCV 2.4. It's too concise and it doesn't contain any explanations.