docs: public DMatrixRMaj getR() {
          DMatrixRMaj R = new DMatrixRMaj(QR.numRows,QR.numCols);
          int N = Math.min(QR.numCols,QR.numRows);
  
          for( int i = 0; i < N; i++ ) {
              for( int j = i; j < QR.numCols; j++ ) {
                  R.unsafe_set(i,j, QR.unsafe_get(i,j));
              }
          }
  
          return R;
      }