AFAIK, OpenCV is not designed for solving matrix related operation like: multiplication, eigenvalue decomposition or SVD, etc., so your result is not surprise to me. For your problem, there two kinds of choice: the first choice is using a dedicated library, lapack or Eigen is recommended, the second one is using a wrapped library, such as Armadillo or CVMlib. I have tested all of them, or you can see more at this, and my choice is lapack, which gives the fastest speed (on Windows, with VS IDE). Hope this help.
