Many of the supporting functions to the ml library are not documented. For example:

* calc_error is not described in CvStatModel [[CvStatModel]]
** float calc_error( CvMLData* [[CvMLData]]* trainData, int type, std::vector<float> *resp = 0 );
** This is used in .../samples/c/tree_engine.cpp

* CvMLData [[CvMLData]] is not documented
* CvTrainTestSplit [[CvTrainTestSplit]] is not documented