public QRDecomposition (Matrix A) {
      // Initialize.
      QR = A.getArrayCopy();
      m = A.getRowDimension();
      n = A.getColumnDimension();
      Rdiag = new double[n];

      // Main loop.
      for (int k = 0; k < n; k++) {
         // Compute 2-norm of k-th column without under/overflow.
         double nrm = 0;
         for (int i = k; i < m; i++) {
            nrm = Maths.hypot(nrm,QR[i][k]);
         }

         if (nrm != 0.0) {
            // Form k-th Householder vector.
            if (QR[k][k] < 0) {
               nrm = -nrm;
            }
            for (int i = k; i < m; i++) {
               QR[i][k] /= nrm;
            }
            QR[k][k] += 1.0;

            // Apply transformation to remaining columns.
            for (int j = k+1; j < n; j++) {
               double s = 0.0; 
               for (int i = k; i < m; i++) {
                  s += QR[i][k]*QR[i][j];
               }
               s = -s/QR[k][k];
               for (int i = k; i < m; i++) {
                  QR[i][j] += s*QR[i][k];
               }
            }
         }
         Rdiag[k] = -nrm;
      }
   }