code: public double norm()
      {
          double sum = 0;
  
          for (int r = 0; r < nRows; ++r) {
              for (int c = 0; c < nCols; ++c) {
                  double v = values[r][c];
                  sum += v*v;
              }
          }
  
          return (double) Math.sqrt(sum);
      }
docs: Compute the Euclidean norm of this matrix.
  @return the norm