fix a preditor bug: rank of matrix is not correct using numpy, see the bug in detail with the link:http://stackoverflow.com/questions/15067538/why-are-the-inverse-results-not-equal, http://math.stackexchange.com/questions/313892/why-are-the-inverse-results-not-equal, http://mathematica.stackexchange.com/questions/20169/why-are-the-inverse-results-not-equal