code: def log_K(Z, X, t):
      
      m, L = update_params(X, t)
      z = Z['x']
      return np.log(det(L))-la.norm(np.dot(L.T,z-m))**2/2.
docs: Log K
          Log of the proposal probability density function for gnm
      Inputs :
          Z :
              proposed to
          x : 
              proposed from 
      Outputs :   
          log of the probability density function