docs: public Vec getRow(int r)
      {
          if(r < 0 || r >= rows())
              throw new ArithmeticException("Row was not a valid value " + r + " not in [0," + (rows()-1) + "]");
          DenseVector c = new DenseVector(cols());
          for(int j =0; j < cols(); j++)
              c.set(j, get(r, j));
          return c;
      }