code: def vorticity(u, v, dx, dy):
      r
      dudy = first_derivative(u, delta=dy, axis=-2)
      dvdx = first_derivative(v, delta=dx, axis=-1)
      return dvdx - dudy
docs: r"""Calculate the vertical vorticity of the horizontal wind.
  
      Parameters
      ----------
      u : (M, N) ndarray
          x component of the wind
      v : (M, N) ndarray
          y component of the wind
      dx : float or ndarray
          The grid spacing(s) in the x-direction. If an array, there should be one item less than
          the size of `u` along the applicable axis.
      dy : float or ndarray
          The grid spacing(s) in the y-direction. If an array, there should be one item less than
          the size of `u` along the applicable axis.
  
      Returns
      -------
      (M, N) ndarray
          vertical vorticity
  
      See Also
      --------
      divergence
  
      Notes
      -----
      If inputs have more than two dimensions, they are assumed to have either leading dimensions
      of (x, y) or trailing dimensions of (y, x), depending on the value of ``dim_order``.