code: def plot_posterior_contour(self, idx_param1=0, idx_param2=1, res1=100, res2=100, smoothing=0.01):
          
          return plt.contour(*self.posterior_mesh(idx_param1, idx_param2, res1, res2, smoothing))
docs: Plots a contour of the kernel density estimation
          of a 2D projection of the current posterior distribution.
  
          :param int idx_param1: Parameter to be treated as :math:`x` when
              plotting.
          :param int idx_param2: Parameter to be treated as :math:`y` when
              plotting.
          :param int res1: Resolution along the :math:`x` direction.
          :param int res2: Resolution along the :math:`y` direction.
          :param float smoothing: Standard deviation of the Gaussian kernel
              used to smooth the particle approximation to the current posterior.
  
          .. seealso::
  
              :meth:`SMCUpdater.posterior_mesh`