/afs/cern.ch/work/a/aaltunda/public/www/CMSSW_6_2_5/src/DataFormats/Math/interface/ProjectMatrix.h

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#ifndef DataFormat_Math_ProjectMatrix_H
#define DataFormat_Math_ProjectMatrix_H

#include "Math/SMatrix.h"



template<typename T, unsigned int N, unsigned int D>
struct ProjectMatrix{
  typedef  ROOT::Math::SMatrix<T,D,D,ROOT::Math::MatRepSym<T,D> > SMatDD;
  typedef  ROOT::Math::SMatrix<T,N,N > SMatNN;
  typedef  ROOT::Math::SMatrix<T,N,D > SMatND;
  
  // no constructor
  
  // H*S
  SMatND project(SMatDD const & s) {
    SMatND r;
    for (unsigned int i=0; i<D; i++)
      for (unsigned int j=0; j<D; j++)
        r(index[i],j) = s(i,j);
    return r;
  }
  
  // K*H
  SMatNN project(SMatND const & k) {
    SMatNN s;
    for (unsigned int i=0; i<N; i++)
      for (unsigned int j=0; j<D; j++)
        s(i,index[j]) = k(i,j);
    return s;
  }

  // S-K*H
  void projectAndSubtractFrom(SMatNN & __restrict__ s, SMatND const & __restrict__ k) {
    for (unsigned int i=0; i<N; i++)
      for (unsigned int j=0; j<D; j++)
        s(i,index[j]) -= k(i,j);
  }

  // only H(i,index(i))=1.
  unsigned int index[D];

};


#endif