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

def log_K(Z, X, t):
    """
    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
    """
    m, L = update_params(X, t)
    z = Z['x']
    return np.log(det(L))-la.norm(np.dot(L.T,z-m))**2/2.