    // @(#)root/matrix:$Name:  $:$Id: TMatrixDSym.cxx,v 1.17 2004/06/22 19:57:01 brun Exp $
    // Authors: Fons Rademakers, Eddy Offermann  Nov 2003

    /*************************************************************************
     * Copyright (C) 1995-2000, Rene Brun and Fons Rademakers.               *
     * All rights reserved.                                                  *
     *                                                                       *
     * For the licensing terms see $ROOTSYS/LICENSE.                         *
     * For the list of contributors see $ROOTSYS/README/CREDITS.             *
     *************************************************************************/

    //////////////////////////////////////////////////////////////////////////
    //                                                                      //
    // TMatrixDSym                                                          //
    //                                                                      //
    // Implementation of a symmetric matrix in the linear algebra package   //
    //                                                                      //
    // Note that in this implementation both matrix element m[i][j] and     //
    // m[j][i] are updated and stored in memory . However, when making the  //
    // object persistent only the upper right triangle is stored .          //
    //                                                                      //
    //////////////////////////////////////////////////////////////////////////

    #include "TMatrixDSym.h"
    #include "TDecompLU.h"
    #include "TMatrixDSymEigen.h"

    ClassImp(TMatrixDSym)

    //______________________________________________________________________________
     TMatrixDSym::TMatrixDSym(Int_t no_rows)
    {
      Allocate(no_rows,no_rows,0,0,1);
    }

    //______________________________________________________________________________
     TMatrixDSym::TMatrixDSym(Int_t row_lwb,Int_t row_upb)
    {
      const Int_t no_rows = row_upb-row_lwb+1;
      Allocate(no_rows,no_rows,row_lwb,row_lwb,1);
    }

    //______________________________________________________________________________
     TMatrixDSym::TMatrixDSym(Int_t no_rows,const Double_t *elements,Option_t *option)
    {
      // option="F": array elements contains the matrix stored column-wise
      //             like in Fortran, so a[i,j] = elements[i+no_rows*j],
      // else        it is supposed that array elements are stored row-wise
      //             a[i,j] = elements[i*no_cols+j]
      //
      // array elements are copied

      Allocate(no_rows,no_rows);
      SetMatrixArray(elements,option);
      if (!IsSymmetric()) {
        Error("TMatrixDSym(Int_t,Double_t*,Option_t*)","matrix not symmetric");
        Invalidate();
      }
    }

    //______________________________________________________________________________
     TMatrixDSym::TMatrixDSym(Int_t row_lwb,Int_t row_upb,const Double_t *elements,Option_t *option)
    {
      // array elements are copied

      const Int_t no_rows = row_upb-row_lwb+1;
      Allocate(no_rows,no_rows,row_lwb,row_lwb);
      SetMatrixArray(elements,option);
      if (!IsSymmetric()) {
        Error("TMatrixDSym(Int_t,Int_t,Double_t*,Option_t*)","matrix not symmetric");
        Invalidate();
      }
    }

    //______________________________________________________________________________
     TMatrixDSym::TMatrixDSym(const TMatrixDSym &another) : TMatrixDBase()
    {
      Assert(another.IsValid());
      Allocate(another.GetNrows(),another.GetNcols(),another.GetRowLwb(),another.GetColLwb());
      *this = another;
    }

    //______________________________________________________________________________
     TMatrixDSym::TMatrixDSym(const TMatrixFSym &another) : TMatrixDBase()
    {
      Assert(another.IsValid());
      Allocate(another.GetNrows(),another.GetNcols(),another.GetRowLwb(),another.GetColLwb());
      *this = another;
    }

    //______________________________________________________________________________
     TMatrixDSym::TMatrixDSym(EMatrixCreatorsOp1 op,const TMatrixDSym &prototype)
    {
      // Create a matrix applying a specific operation to the prototype.
      // Example: TMatrixDSym a(10,12); ...; TMatrixDSym b(TMatrixDBase::kTransposed, a);
      // Supported operations are: kZero, kUnit, and kTransposed .

      Assert(this != &prototype);
      Invalidate();

      Assert(prototype.IsValid());

      switch(op) {
        case kZero:
          Allocate(prototype.GetNrows(),prototype.GetNcols(),
                   prototype.GetRowLwb(),prototype.GetColLwb(),1);
          break;

        case kUnit:
          Allocate(prototype.GetNrows(),prototype.GetNcols(),
                   prototype.GetRowLwb(),prototype.GetColLwb(),1);
          UnitMatrix();
          break;

        case kTransposed:
          Allocate(prototype.GetNcols(), prototype.GetNrows(),
                   prototype.GetColLwb(),prototype.GetRowLwb());
          Transpose(prototype);
          break;

        case kAtA:
          AtMultA(prototype);
          break;

        default:
          Error("TMatrixDSym(EMatrixCreatorOp1,const TMatrixDSym)",
                 "operation %d not yet implemented", op);
      }
    }

    //______________________________________________________________________________
     TMatrixDSym::TMatrixDSym(EMatrixCreatorsOp1 op,const TMatrixD &prototype)
    {
      Assert(dynamic_cast<TMatrixD *>(this) != &prototype);
      Invalidate();

      Assert(prototype.IsValid());

      switch(op) {
        case kAtA:
          AtMultA(prototype);
          break;

        default:
          Error("TMatrixDSym(EMatrixCreatorOp1,const TMatrixD)",
                 "operation %d not yet implemented", op);
      }
    }

    //______________________________________________________________________________
     TMatrixDSym::TMatrixDSym(const TMatrixDSymLazy &lazy_constructor)
    {
      Allocate(lazy_constructor.GetRowUpb()-lazy_constructor.GetRowLwb()+1,
               lazy_constructor.GetRowUpb()-lazy_constructor.GetRowLwb()+1,
               lazy_constructor.GetRowLwb(),lazy_constructor.GetRowLwb(),1);
      lazy_constructor.FillIn(*this);
      if (!IsSymmetric()) {
        Error("TMatrixDSym(TMatrixDSymLazy)","matrix not symmetric");
        Invalidate();
      }
    }

    //______________________________________________________________________________
     void TMatrixDSym::Allocate(Int_t no_rows,Int_t no_cols,Int_t row_lwb,Int_t col_lwb,
                               Int_t init,Int_t /*nr_nonzeros*/)
    {
      // Allocate new matrix. Arguments are number of rows, columns, row
      // lowerbound (0 default) and column lowerbound (0 default).

      if (no_rows < 0 || no_cols < 0)
      {
        Error("Allocate","no_rows=%d no_cols=%d",no_rows,no_cols);
        Invalidate();
        return;
      }

      MakeValid();
      fNrows   = no_rows;
      fNcols   = no_cols;
      fRowLwb  = row_lwb;
      fColLwb  = col_lwb;
      fNelems  = fNrows*fNcols;
      fIsOwner = kTRUE;
      fTol     = DBL_EPSILON;

      if (fNelems > 0) {
        fElements = New_m(fNelems);
        if (init)
          memset(fElements,0,fNelems*sizeof(Double_t));
      } else
        fElements = 0;
    }

    //______________________________________________________________________________
     void TMatrixDSym::AtMultA(const TMatrixD &a,Int_t constr)
    {
      // Create a matrix C such that C = A' * A. In other words,
      // c[i,j] = SUM{ a[k,i] * a[k,j] }. Note, matrix C is allocated for constr=1.

      Assert(a.IsValid());

      if (constr)
        Allocate(a.GetNcols(),a.GetNcols(),a.GetColLwb(),a.GetColLwb(),1);

    #ifdef CBLAS
      const Double_t *ap = a.GetMatrixArray();
            Double_t *cp = this->GetMatrixArray();
      cblas_dgemm (CblasRowMajor,CblasTrans,CblasNoTrans,fNrows,fNcols,a.GetNrows(),
                   1.0,ap,a.GetNcols(),ap,a.GetNcols(),1.0,cp,fNcols);
    #else
      const Int_t nb     = a.GetNoElements();
      const Int_t ncolsa = a.GetNcols();
      const Int_t ncolsb = ncolsa;
      const Double_t * const ap = a.GetMatrixArray();
      const Double_t * const bp = ap;
            Double_t *       cp = this->GetMatrixArray();

      const Double_t *acp0 = ap;           // Pointer to  A[i,0];
      while (acp0 < ap+a.GetNcols()) {
        for (const Double_t *bcp = bp; bcp < bp+ncolsb; ) { // Pointer to the j-th column of A, Start bcp = A[0,0]
          const Double_t *acp = acp0;                       // Pointer to the i-th column of A, reset to A[0,i]
          Double_t cij = 0;
          while (bcp < bp+nb) {           // Scan the i-th column of A and
            cij += *acp * *bcp;           // the j-th col of A
            acp += ncolsa;
            bcp += ncolsb;
          }
          *cp++ = cij;
          bcp -= nb-1;                    // Set bcp to the (j+1)-th col
        }
        acp0++;                           // Set acp0 to the (i+1)-th col
      }

      Assert(cp == this->GetMatrixArray()+fNelems && acp0 == ap+ncolsa);
    #endif
    }

    //______________________________________________________________________________
     void TMatrixDSym::AtMultA(const TMatrixDSym &a,Int_t constr)
    {
      // Matrix multiplication, with A symmetric
      // Create a matrix C such that C = A' * A = A * A = A * A'
      // Note, matrix C is allocated for constr=1.

      Assert(a.IsValid());

      if (constr)
        Allocate(a.GetNcols(),a.GetNcols(),a.GetColLwb(),a.GetColLwb(),1);

      const Double_t *ap1 = a.GetMatrixArray();
      const Double_t *bp1 = ap1;
            Double_t *cp1 = this->GetMatrixArray();

    #ifdef CBLAS
      cblas_dsymm (CblasRowMajor,CblasLeft,CblasUpper,fNrows,fNcols,1.0,
                   ap1,a.GetNcols(),bp1,a.GetNcols(),0.0,cp1,fNcols);
    #else
      const Double_t *ap2 = a.GetMatrixArray();
      const Double_t *bp2 = ap2;
            Double_t *cp2 = this->GetMatrixArray();
      for (Int_t i = 0; i < fNrows; i++) {
        for (Int_t j = 0; j < fNcols; j++) {
          const Double_t b_ij = *bp1++;
          *cp1 += b_ij*(*ap1);
          Double_t tmp = 0.0;
          ap2 = ap1+1;
          for (Int_t k = i+1; k < fNrows; k++) {
            const Int_t index_kj = k*fNcols+j;
            const Double_t a_ik = *ap2++;
            const Double_t b_kj = bp2[index_kj];
            cp2[index_kj] += a_ik*b_ij;
            tmp += a_ik*b_kj;
          }
          *cp1++ += tmp;
        }
        ap1 += fNrows+1;
      }
    #endif
    }

    //______________________________________________________________________________
     TMatrixDSym &TMatrixDSym::Use(Int_t row_lwb,Int_t row_upb,Double_t *data)
    {
      if (row_upb < row_lwb)
      {
        Error("Use","row_upb=%d < row_lwb=%d",row_upb,row_lwb);
        Invalidate();
        return *this;
      }

      Clear();
      fNrows    = row_upb-row_lwb+1;
      fNcols    = fNrows;
      fRowLwb   = row_lwb;
      fColLwb   = row_lwb;
      fNelems   = fNrows*fNcols;
      fElements = data;
      fIsOwner  = kFALSE;

      return *this;
    }

    //______________________________________________________________________________
     TMatrixDSym &TMatrixDSym::GetSub(Int_t row_lwb,Int_t row_upb,TMatrixDSym &target,Option_t *option) const
    {
      // Get submatrix [row_lwb..row_upb][row_lwb..row_upb]; The indexing range of the
      // returned matrix depends on the argument option:
      //
      // option == "S" : return [0..row_upb-row_lwb+1][0..row_upb-row_lwb+1] (default)
      // else          : return [row_lwb..row_upb][row_lwb..row_upb]

      Assert(IsValid());

      if (row_lwb < fRowLwb || row_lwb > fRowLwb+fNrows-1) {
        Error("GetSub","row_lwb out of bounds");
        target.Invalidate();
        return target;
      }
      if (row_upb < fRowLwb || row_upb > fRowLwb+fNrows-1) {
        Error("GetSub","row_upb out of bounds");
        target.Invalidate();
        return target;
      }
      if (row_upb < row_lwb) {
        Error("GetSub","row_upb < row_lwb");
        target.Invalidate();
        return target;
      }

      TString opt(option);
      opt.ToUpper();
      const Int_t shift = (opt.Contains("S")) ? 1 : 0;

      Int_t row_lwb_sub;
      Int_t row_upb_sub;
      if (shift) {
        row_lwb_sub = 0;
        row_upb_sub = row_upb-row_lwb;
      } else {
        row_lwb_sub = row_lwb;
        row_upb_sub = row_upb;
      }

      target.ResizeTo(row_lwb_sub,row_upb_sub,row_lwb_sub,row_upb_sub);
      const Int_t nrows_sub = row_upb_sub-row_lwb_sub+1;

      if (target.GetRowIndexArray() && target.GetColIndexArray()) {
        for (Int_t irow = 0; irow < nrows_sub; irow++) {
          for (Int_t icol = 0; icol < nrows_sub; icol++) {
            target(irow+row_lwb_sub,icol+row_lwb_sub) = (*this)(row_lwb+irow,row_lwb+icol);
          }
        }
      } else {
        const Double_t *ap = this->GetMatrixArray()+(row_lwb-fRowLwb)*fNrows+(row_lwb-fRowLwb);
              Double_t *bp = target.GetMatrixArray();

        for (Int_t irow = 0; irow < nrows_sub; irow++) {
          const Double_t *ap_sub = ap;
          for (Int_t icol = 0; icol < nrows_sub; icol++) {
            *bp++ = *ap_sub++;
          }
          ap += fNrows;
        }
      }

      return target;
    }

    //______________________________________________________________________________
     TMatrixDBase &TMatrixDSym::GetSub(Int_t row_lwb,Int_t row_upb,Int_t col_lwb,Int_t col_upb,
                                      TMatrixDBase &target,Option_t *option) const
    {
      // Get submatrix [row_lwb..row_upb][col_lwb..col_upb]; The indexing range of the
      // returned matrix depends on the argument option:
      //
      // option == "S" : return [0..row_upb-row_lwb+1][0..col_upb-col_lwb+1] (default)
      // else          : return [row_lwb..row_upb][col_lwb..col_upb]

      Assert(IsValid());
      if (row_lwb < fRowLwb || row_lwb > fRowLwb+fNrows-1) {
        Error("GetSub","row_lwb out of bounds");
        target.Invalidate();
        return target;
      }
      if (col_lwb < fColLwb || col_lwb > fColLwb+fNcols-1) {
        Error("GetSub","col_lwb out of bounds");
        target.Invalidate();
        return target;
      }
      if (row_upb < fRowLwb || row_upb > fRowLwb+fNrows-1) {
        Error("GetSub","row_upb out of bounds");
        target.Invalidate();
        return target;
      }
      if (col_upb < fColLwb || col_upb > fColLwb+fNcols-1) {
        Error("GetSub","col_upb out of bounds");
        target.Invalidate();
        return target;
      }
      if (row_upb < row_lwb || col_upb < col_lwb) {
        Error("GetSub","row_upb < row_lwb || col_upb < col_lwb");
        target.Invalidate();
        return target;
      }

      TString opt(option);
      opt.ToUpper();
      const Int_t shift = (opt.Contains("S")) ? 1 : 0;

      const Int_t row_lwb_sub = (shift) ? 0               : row_lwb;
      const Int_t row_upb_sub = (shift) ? row_upb-row_lwb : row_upb;
      const Int_t col_lwb_sub = (shift) ? 0               : col_lwb;
      const Int_t col_upb_sub = (shift) ? col_upb-col_lwb : col_upb;

      target.ResizeTo(row_lwb_sub,row_upb_sub,col_lwb_sub,col_upb_sub);
      const Int_t nrows_sub = row_upb_sub-row_lwb_sub+1;
      const Int_t ncols_sub = col_upb_sub-col_lwb_sub+1;

      if (target.GetRowIndexArray() && target.GetColIndexArray()) {
        for (Int_t irow = 0; irow < nrows_sub; irow++) {
          for (Int_t icol = 0; icol < ncols_sub; icol++) {
            target(irow+row_lwb_sub,icol+col_lwb_sub) = (*this)(row_lwb+irow,col_lwb+icol);
          }
        }
      } else {
        const Double_t *ap = this->GetMatrixArray()+(row_lwb-fRowLwb)*fNcols+(col_lwb-fColLwb);
              Double_t *bp = target.GetMatrixArray();

        for (Int_t irow = 0; irow < nrows_sub; irow++) {
          const Double_t *ap_sub = ap;
          for (Int_t icol = 0; icol < ncols_sub; icol++) {
            *bp++ = *ap_sub++;
          }
          ap += fNcols;
        }
      }

      return target;
    }

    //______________________________________________________________________________
     TMatrixDSym &TMatrixDSym::SetSub(Int_t row_lwb,const TMatrixDBase &source)
    {
      // Insert matrix source starting at [row_lwb][row_lwb], thereby overwriting the part
      // [row_lwb..row_lwb+nrows_source][row_lwb..row_lwb+nrows_source];

      Assert(IsValid());
      Assert(source.IsValid());

      if (!source.IsSymmetric()) {
        Error("SetSub","source matrix is not symmetric");
        Invalidate();
        return *this;
      }
      if (row_lwb < fRowLwb || row_lwb > fRowLwb+fNrows-1) {
        Error("SetSub","row_lwb outof bounds");
        Invalidate();
        return *this;
      }
      const Int_t nRows_source = source.GetNrows();
      if (row_lwb+nRows_source > fRowLwb+fNrows) {
        Error("SetSub","source matrix too large");
        Invalidate();
        return *this;
      }

      if (source.GetRowIndexArray() && source.GetColIndexArray()) {
        const Int_t rowlwb_s = source.GetRowLwb();
        for (Int_t irow = 0; irow < nRows_source; irow++) {
          for (Int_t icol = 0; icol < nRows_source; icol++) {
            (*this)(row_lwb+irow,row_lwb+icol) = source(rowlwb_s+irow,rowlwb_s+icol);
          }
        }
      } else {
        const Double_t *bp = source.GetMatrixArray();
              Double_t *ap = this->GetMatrixArray()+(row_lwb-fRowLwb)*fNrows+(row_lwb-fRowLwb);

        for (Int_t irow = 0; irow < nRows_source; irow++) {
          Double_t *ap_sub = ap;
          for (Int_t icol = 0; icol < nRows_source; icol++) {
            *ap_sub++ = *bp++;
          }
          ap += fNrows;
        }
      }

      return *this;
    }

    //______________________________________________________________________________
     TMatrixDBase &TMatrixDSym::SetSub(Int_t row_lwb,Int_t col_lwb,const TMatrixDBase &source)
    {
      // Insert matrix source starting at [row_lwb][col_lwb] in a symmetric fashion, thereby overwriting the part
      // [row_lwb..row_lwb+nrows_source][row_lwb..row_lwb+nrows_source];

      Assert(IsValid());
      Assert(source.IsValid());

      if (row_lwb < fRowLwb || row_lwb > fRowLwb+fNrows-1) {
        Error("SetSub","row_lwb out of bounds");
        Invalidate();
        return *this;
      }
      if (col_lwb < fColLwb || col_lwb > fColLwb+fNcols-1) {
        Error("SetSub","col_lwb out of bounds");
        Invalidate();
        return *this;
      }
      const Int_t nRows_source = source.GetNrows();
      const Int_t nCols_source = source.GetNcols();

      if (row_lwb+nRows_source > fRowLwb+fNrows || col_lwb+nCols_source > fRowLwb+fNrows) {
        Error("SetSub","source matrix too large");
        Invalidate();
        return *this;
      }
      if (col_lwb+nCols_source > fRowLwb+fNrows || row_lwb+nRows_source > fRowLwb+fNrows) {
        Error("SetSub","source matrix too large");
        Invalidate();
        return *this;
      }

      const Int_t rowlwb_s = source.GetRowLwb();
      const Int_t collwb_s = source.GetColLwb();
      if (row_lwb >= col_lwb) {
        // lower triangle
        Int_t irow;
        for (irow = 0; irow < nRows_source; irow++) {
          for (Int_t icol = 0; col_lwb+icol <= row_lwb+irow &&
                                 icol < nCols_source; icol++) {
            (*this)(row_lwb+irow,col_lwb+icol) = source(irow+rowlwb_s,icol+collwb_s);
          }
        }

        // upper triangle
        for (irow = 0; irow < nCols_source; irow++) {
          for (Int_t icol = nRows_source-1; row_lwb+icol > irow+col_lwb &&
                                  icol >= 0; icol--) {
            (*this)(col_lwb+irow,row_lwb+icol) = source(icol+rowlwb_s,irow+collwb_s);
          }
        }
      } else {

      }

      return *this;
    }

    //______________________________________________________________________________
     TMatrixDBase &TMatrixDSym::SetMatrixArray(const Double_t *data,Option_t *option)
    {
      TMatrixDBase::SetMatrixArray(data,option);
      if (!this->IsSymmetric()) {
        Error("SetMatrixArray","Matrix is not symmetric after Set");
        Invalidate();
      }

      return *this;
    }

    //______________________________________________________________________________
     TMatrixDBase &TMatrixDSym::Shift(Int_t row_shift,Int_t col_shift)
    {
      if (row_shift != col_shift) {
        Error("Shift","row_shift != col_shift");
        Invalidate();
        return *this;
      }
      return TMatrixDBase::Shift(row_shift,col_shift);
    }

    //______________________________________________________________________________
     TMatrixDBase &TMatrixDSym::ResizeTo(Int_t nrows,Int_t ncols,Int_t /*nr_nonzeros*/)
    {
      if (nrows != ncols) {
        Error("ResizeTo","nrows != ncols");
        Invalidate();
        return *this;
      }
      return TMatrixDBase::ResizeTo(nrows,ncols);
    }

    //______________________________________________________________________________
     TMatrixDBase &TMatrixDSym::ResizeTo(Int_t row_lwb,Int_t row_upb,Int_t col_lwb,Int_t col_upb,
                               Int_t /*nr_nonzeros*/)
    {
      if (row_lwb != col_lwb) {
        Error("ResizeTo","row_lwb != col_lwb");
        Invalidate();
        return *this;
      }
      if (row_upb != col_upb) {
        Error("ResizeTo","row_upb != col_upb");
        Invalidate();
        return *this;
      }
      return TMatrixDBase::ResizeTo(row_lwb,row_upb,col_lwb,col_upb);
    }

    //______________________________________________________________________________
     Double_t TMatrixDSym::Determinant() const
    {
      const TMatrixD &tmp = *this;
      TDecompLU lu(tmp,fTol);
      Double_t d1,d2;
      lu.Det(d1,d2);
      return d1*TMath::Power(2.0,d2);
    }

    //______________________________________________________________________________
     void TMatrixDSym::Determinant(Double_t &d1,Double_t &d2) const
    {
      const TMatrixD &tmp = *this;
      TDecompLU lu(tmp,fTol);
      lu.Det(d1,d2);
    }

    //______________________________________________________________________________
     TMatrixDSym &TMatrixDSym::Transpose(const TMatrixDSym &source)
    {
      // Transpose a matrix.

      Assert(IsValid());
      Assert(source.IsValid());

      if (fNrows != source.GetNcols() || fRowLwb != source.GetColLwb())
      {
        Error("Transpose","matrix has wrong shape");
        Invalidate();
        return *this;
      }

      *this = source;
      return *this;
    }

    //______________________________________________________________________________
    TMatrixDSym &TMatrixDSym::operator=(const TMatrixDSym &source)
    {
      if (!AreCompatible(*this,source)) {
        Error("operator=","matrices not compatible");
        Invalidate();
        return *this;
      }

      if (this != &source) {
        TObject::operator=(source);
        memcpy(this->GetMatrixArray(),source.fElements,fNelems*sizeof(Double_t));
      }
      return *this;
    }

    //______________________________________________________________________________
    TMatrixDSym &TMatrixDSym::operator=(const TMatrixFSym &source)
    {
      if (!AreCompatible(*this,source)) {
        Error("operator=","matrices not compatible");
        Invalidate();
        return *this;
      }

      if (dynamic_cast<TMatrixFSym *>(this) != &source) {
        TObject::operator=(source);
        const Float_t  * const ps = source.GetMatrixArray();
              Double_t * const pt = GetMatrixArray();
        for (Int_t i = 0; i < fNelems; i++)
          pt[i] = (Double_t) ps[i];
        fTol = (Double_t)source.GetTol();
      }

      return *this;
    }

    //______________________________________________________________________________
    TMatrixDSym &TMatrixDSym::operator=(const TMatrixDSymLazy &lazy_constructor)
    {
      Assert(IsValid());

      if (lazy_constructor.fRowUpb != GetRowUpb() ||
          lazy_constructor.fRowLwb != GetRowLwb()) {
         Error("operator=(const TMatrixDSymLazy&)", "matrix is incompatible with "
               "the assigned Lazy matrix");
        Invalidate();
        return *this;
      }

      lazy_constructor.FillIn(*this);
      return *this;
    }

    //______________________________________________________________________________
    TMatrixDSym &TMatrixDSym::operator=(Double_t val)
    {
      // Assign val to every element of the matrix.

      Assert(IsValid());

      Double_t *ep = fElements;
      const Double_t * const ep_last = ep+fNelems;
      while (ep < ep_last)
        *ep++ = val;

      return *this;
    }

    //______________________________________________________________________________
    TMatrixDSym &TMatrixDSym::operator+=(Double_t val)
    {
      // Add val to every element of the matrix.

      Assert(IsValid());

      Double_t *ep = fElements;
      const Double_t * const ep_last = ep+fNelems;
      while (ep < ep_last)
        *ep++ += val;

      return *this;
    }

    //______________________________________________________________________________
    TMatrixDSym &TMatrixDSym::operator-=(Double_t val)
    {
      // Subtract val from every element of the matrix.

      Assert(IsValid());

      Double_t *ep = fElements;
      const Double_t * const ep_last = ep+fNelems;
      while (ep < ep_last)
        *ep++ -= val;

      return *this;
    }

    //______________________________________________________________________________
    TMatrixDSym &TMatrixDSym::operator*=(Double_t val)
    {
      // Multiply every element of the matrix with val.

      Assert(IsValid());

      Double_t *ep = fElements;
      const Double_t * const ep_last = ep+fNelems;
      while (ep < ep_last)
        *ep++ *= val;

      return *this;
    }

    //______________________________________________________________________________
    TMatrixDSym &TMatrixDSym::operator+=(const TMatrixDSym &source)
    {
      // Add the source matrix.

      if (!AreCompatible(*this,source)) {
        Error("operator+=","matrices not compatible");
        Invalidate();
        return *this;
      }

      const Double_t *sp  = source.GetMatrixArray();
            Double_t *trp = this->GetMatrixArray(); // pointer to UR part and diagonal, traverse row-wise
            Double_t *tcp = trp;                 // pointer to LL part,              traverse col-wise
      for (Int_t i = 0; i < fNrows; i++) {
        sp  += i;
        trp += i;         // point to [i,i]
        tcp += i*fNcols;  // point to [i,i]
        for (Int_t j = i; j < fNcols; j++) {
          if (j > i) *tcp += *sp;
          *trp++ += *sp++;
          tcp += fNcols;
        }
        tcp -= fNelems-1; // point to [0,i]
      }

      return *this;
    }

    //______________________________________________________________________________
    TMatrixDSym &TMatrixDSym::operator-=(const TMatrixDSym &source)
    {
      // Subtract the source matrix.

      if (!AreCompatible(*this,source)) {
        Error("operator-=","matrices not compatible");
        Invalidate();
        return *this;
      }

      const Double_t *sp  = source.GetMatrixArray();
            Double_t *trp = this->GetMatrixArray(); // pointer to UR part and diagonal, traverse row-wise
            Double_t *tcp = trp;                 // pointer to LL part,              traverse col-wise
      for (Int_t i = 0; i < fNrows; i++) {
        sp  += i;
        trp += i;         // point to [i,i]
        tcp += i*fNcols;  // point to [i,i]
        for (Int_t j = i; j < fNcols; j++) {
          if (j > i) *tcp -= *sp;
          *trp++ -= *sp++;
          tcp += fNcols;
        }
        tcp -= fNelems-1; // point to [0,i]
      }

      return *this;
    }

    //______________________________________________________________________________
     TMatrixDBase &TMatrixDSym::Apply(const TElementActionD &action)
    {
      Assert(IsValid());

      Double_t val = 0;
      Double_t *trp = this->GetMatrixArray(); // pointer to UR part and diagonal, traverse row-wise
      Double_t *tcp = trp;                 // pointer to LL part,              traverse col-wise
      for (Int_t i = 0; i < fNrows; i++) {
        trp += i;         // point to [i,i]
        tcp += i*fNcols;  // point to [i,i]
        for (Int_t j = i; j < fNcols; j++) {
          action.Operation(val);
          if (j > i) *tcp = val;
          *trp++ = val;
          tcp += fNcols;
        }
        tcp -= fNelems-1; // point to [0,i]
      }

      return *this;
    }

    //______________________________________________________________________________
     TMatrixDBase &TMatrixDSym::Apply(const TElementPosActionD &action)
    {
      // Apply action to each element of the matrix. To action the location
      // of the current element is passed.

      Assert(IsValid());

      Double_t val = 0;
      Double_t *trp = this->GetMatrixArray(); // pointer to UR part and diagonal, traverse row-wise
      Double_t *tcp = trp;                 // pointer to LL part,              traverse col-wise
      for (Int_t i = 0; i < fNrows; i++) {
        action.fI = i+fRowLwb;
        trp += i;         // point to [i,i]
        tcp += i*fNcols;  // point to [i,i]
        for (Int_t j = i; j < fNcols; j++) {
          action.fJ = j+fColLwb;
          action.Operation(val);
          if (j > i) *tcp = val;
          *trp++ = val;
          tcp += fNcols;
        }
        tcp -= fNelems-1; // point to [0,i]
      }

      return *this;
    }

    //______________________________________________________________________________
     TMatrixDBase &TMatrixDSym::Randomize(Double_t alpha,Double_t beta,Double_t &seed)
    {
      // randomize matrix element values but keep matrix symmetric

      Assert(IsValid());

      if (fNrows != fNcols || fRowLwb != fColLwb) {
        Error("Randomize(Double_t,Double_t,Double_t &","matrix should be square");
        Invalidate();
        return *this;
      }

      const Double_t scale = beta-alpha;
      const Double_t shift = alpha/scale;

      Double_t *ep = GetMatrixArray();
      for (Int_t i = 0; i < fNrows; i++) {
        const Int_t off = i*fNcols;
        for (Int_t j = 0; j <= i; j++) {
          ep[off+j] = scale*(Drand(seed)+shift);
          if (i != j) {
            ep[j*fNcols+i] = ep[off+j];
          }
        }
      }

      return *this;
    }

    //______________________________________________________________________________
     TMatrixDSym &TMatrixDSym::RandomizePD(Double_t alpha,Double_t beta,Double_t &seed)
    {
      // randomize matrix element values but keep matrix symmetric positive definite

      Assert(IsValid());

      if (fNrows != fNcols || fRowLwb != fColLwb) {
        Error("RandomizeSym(Double_t,Double_t,Double_t &","matrix should be square");
        Invalidate();
        return *this;
      }

      const Double_t scale = beta-alpha;
      const Double_t shift = alpha/scale;

      Double_t *ep = GetMatrixArray();
      Int_t i;
      for (i = 0; i < fNrows; i++) {
        const Int_t off = i*fNcols;
        for (Int_t j = 0; j <= i; j++)
          ep[off+j] = scale*(Drand(seed)+shift);
      }

      for (i = fNrows-1; i >= 0; i--) {
        const Int_t off1 = i*fNcols;
        for (Int_t j = i; j >= 0; j--) {
          const Int_t off2 = j*fNcols;
          ep[off1+j] *= ep[off2+j];
          for (Int_t k = j-1; k >= 0; k--) {
            ep[off1+j] += ep[off1+k]*ep[off2+k];
          }
          if (i != j)
            ep[off2+i] = ep[off1+j];
        }
      }

      return *this;
    }

    //______________________________________________________________________________
     const TMatrixD TMatrixDSym::EigenVectors(TVectorD &eigenValues) const
    {
      // Return a matrix containing the eigen-vectors ordered by descending eigen-values.
      // For full functionality use TMatrixDSymEigen .

      TMatrixDSymEigen eigen(*this);
      eigenValues = eigen.GetEigenValues();
      return eigen.GetEigenVectors();
    }

    //______________________________________________________________________________
    Bool_t operator==(const TMatrixDSym &m1,const TMatrixDSym &m2)
    {
      // Check to see if two matrices are identical.

      if (!AreCompatible(m1,m2)) return kFALSE;
      return (memcmp(m1.GetMatrixArray(),m2.GetMatrixArray(),
                     m1.GetNoElements()*sizeof(Double_t)) == 0);
    }

    //______________________________________________________________________________
    TMatrixDSym operator+(const TMatrixDSym &source1,const TMatrixDSym &source2)
    {
      TMatrixDSym target(source1);
      target += source2;
      return target;
    }

    //______________________________________________________________________________
    TMatrixDSym operator-(const TMatrixDSym &source1,const TMatrixDSym &source2)
    {
      TMatrixDSym target(source1);
      target -= source2;
      return target;
    }

    //______________________________________________________________________________
    TMatrixDSym operator*(Double_t val,const TMatrixDSym &source)
    {
      TMatrixDSym target(source);
      target *= val;
      return target;
    }

    //______________________________________________________________________________
    TMatrixDSym operator*(const TMatrixDSym &source,Double_t val)
    {
      TMatrixDSym target(source);
      target *= val;
      return target;
    }

    //______________________________________________________________________________
    TMatrixDSym &Add(TMatrixDSym &target,Double_t scalar,const TMatrixDSym &source)
    {
      // Modify addition: target += scalar * source.

      if (!AreCompatible(target,source)) {
        ::Error("Add","matrices not compatible");
        target.Invalidate();
        return target;
      }

      const Int_t nrows   = target.GetNrows();
      const Int_t ncols   = target.GetNcols();
      const Int_t nelems  = target.GetNoElements();
      const Double_t *sp  = source.GetMatrixArray();
            Double_t *trp = target.GetMatrixArray(); // pointer to UR part and diagonal, traverse row-wise
            Double_t *tcp = target.GetMatrixArray(); // pointer to LL part,              traverse col-wise
      for (Int_t i = 0; i < nrows; i++) {
        sp  += i;
        trp += i;        // point to [i,i]
        tcp += i*ncols;  // point to [i,i]
        for (Int_t j = i; j < ncols; j++) {
          const Double_t tmp = scalar * *sp++;
          if (j > i) *tcp += tmp;
          *trp++ += tmp;
          tcp += ncols;
        }
        tcp -= nelems-1; // point to [0,i]
      }

      return target;
    }

    //______________________________________________________________________________
    TMatrixDSym &ElementMult(TMatrixDSym &target,const TMatrixDSym &source)
    {
      // Multiply target by the source, element-by-element.

      if (!AreCompatible(target,source)) {
        ::Error("ElementMult","matrices not compatible");
        target.Invalidate();
        return target;
      }

      const Int_t nrows   = target.GetNrows();
      const Int_t ncols   = target.GetNcols();
      const Int_t nelems  = target.GetNoElements();
      const Double_t *sp  = source.GetMatrixArray();
            Double_t *trp = target.GetMatrixArray(); // pointer to UR part and diagonal, traverse row-wise
            Double_t *tcp = target.GetMatrixArray(); // pointer to LL part,              traverse col-wise
      for (Int_t i = 0; i < nrows; i++) {
        sp  += i;
        trp += i;        // point to [i,i]
        tcp += i*ncols;  // point to [i,i]
        for (Int_t j = i; j < ncols; j++) {
          if (j > i) *tcp *= *sp;
          *trp++ *= *sp++;
          tcp += ncols;
        }
        tcp -= nelems-1; // point to [0,i]
      }

      return target;
    }

    //______________________________________________________________________________
    TMatrixDSym &ElementDiv(TMatrixDSym &target,const TMatrixDSym &source)
    {
      // Multiply target by the source, element-by-element.

      if (!AreCompatible(target,source)) {
        ::Error("ElementDiv","matrices not compatible");
        target.Invalidate();
        return target;
      }

      const Int_t nrows   = target.GetNrows();
      const Int_t ncols   = target.GetNcols();
      const Int_t nelems  = target.GetNoElements();
      const Double_t *sp  = source.GetMatrixArray();
            Double_t *trp = target.GetMatrixArray(); // pointer to UR part and diagonal, traverse row-wise
            Double_t *tcp = target.GetMatrixArray(); // pointer to LL part,              traverse col-wise
      for (Int_t i = 0; i < nrows; i++) {
        sp  += i;
        trp += i;        // point to [i,i]
        tcp += i*ncols;  // point to [i,i]
        for (Int_t j = i; j < ncols; j++) {
          Assert(*sp != 0.0);
          if (j > i) *tcp /= *sp;
          *trp++ /= *sp++;
          tcp += ncols;
        }
        tcp -= nelems-1; // point to [0,i]
      }

      return target;
    }

    //______________________________________________________________________________
     void TMatrixDSym::Streamer(TBuffer &R__b)
    {
      // Stream an object of class TMatrixDSym.

      if (R__b.IsReading()) {
        UInt_t R__s, R__c;
        Version_t R__v = R__b.ReadVersion(&R__s, &R__c);
        Clear();
        TMatrixDBase::Class()->ReadBuffer(R__b,this,R__v,R__s,R__c);
        fElements = new Double_t[fNelems];
        Int_t i;
        for (i = 0; i < fNrows; i++) {
          R__b.ReadFastArray(fElements+i*fNcols+i,fNcols-i);
        }
        // copy to Lower left triangle
        for (i = 0; i < fNrows; i++) {
          for (Int_t j = 0; j < i; j++) {
            fElements[i*fNcols+j] = fElements[j*fNrows+i];
          }
        }
        if (fNelems <= kSizeMax) {
          memcpy(fDataStack,fElements,fNelems*sizeof(Double_t));
          delete [] fElements;
          fElements = fDataStack;
        }
      } else {
        TMatrixDBase::Class()->WriteBuffer(R__b,this);
        // Only write the Upper right triangle
        for (Int_t i = 0; i < fNrows; i++) {
          R__b.WriteFastArray(fElements+i*fNcols+i,fNcols-i);
        }
      }
    }