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