Fix svm examples (Bug #4096)

[dhood]

No description provided.

[vpisarev]

@dhood, thanks for the patch! I'd suggest to use a bit different solution though. The performance increase when using a single compressed support vector is so dramatic that I would always use it. What we can do is to add another field in SVMImpl, "Mat compressed_sv", which is computed and used for prediction when we train/load linear SVM. In other words, optimize_linear can be done not in-place. With your patch, however, user needs to make this principal decision, whether he/she wants a fast prediction or wants to get the real support vectors.

Also, I'm not sure if your patch handles "load svm from file" case correctly. At least, I do not see where useCompressedSV is written or read.

[dhood]

@vpisarev, I agree - I originally had implemented it as you propose and added a parameter to getSupportVectors so that the user could get the raw SVs or the compressed one, but when I saw your comment on #3881 I changed approach. I will change it back to as you suggest, and will just simply not pass any option to getSupportVectors.

If your comment does not apply at this point in time, I will add an option to retrieve the compressed vector (or an additional method)

[dhood]

Bump

[vpisarev]

@dhood, sorry for delay. As I see, uncompressed_sv's are not stored in XML, which probably means that after save & load the function getSupportVectors(false) will not work as expected

[dhood]

now I apologise for the delay! went overseas, which is the only reason I was 'bump'ing earlier.
not sure if you have any suggestions around the ABI compliance error. just wait till the next release? thanks for the advice

[vpisarev]

see #5783