TPrincipal.
The user interface is in TTree::Principal that calls the TTreePlayer::Principal
function. The specs of this interface are:
TPrincipal *TTree::Principal(const char *varexp, const char *selection, Option_t *option, Int_t nentries, Int_t firstentry)
{
//*-*-*-*-*-*-*-*-*Interface to the Principal Components Analysis class*-*-*
//*-*              ====================================================
//
//   Create an instance of TPrincipal
//   Fill it with the selected variables
//   if option "n" is specified, the TPrincipal object is filled with
//                 normalized variables.
//   If option "p" is specified, compute the principal components
//   If option "p" and "d" print results of analysis
//   If option "p" and "h" generate standard histograms
//   If option "p" and "c" generate code of conversion functions
//   return a pointer to the TPrincipal object. It is the user responsability
//   to delete this object.
//   The option default value is "np"
//
//   see TTree::Draw for explanation of the other parameters.
//
//   The created object is  named "principal" and a reference to it
//   is added to the list of specials Root objects.
//   you can retrieve a pointer to the created object via:
//      TPrincipal *principal =
//        (TPrincipal*)gROOT->GetListOfSpecials()->FindObject("principal");
//


git-svn-id: http://root.cern.ch/svn/root/trunk@489 27541ba8-7e3a-0410-8455-c3a389f83636