function Nst=DiffShapeFun(s,t)   
    % 关于 s 求导 
    N1s=(s/4 - 1/4)*(t + 1) + ((t + 1)*(s - t + 1))/4; 
    N2s=-(s/4 - 1/4)*(t - 1) - ((t - 1)*(s + t + 1))/4; 
    N3s=((t - 1)*(t - s + 1))/4 - (s/4 + 1/4)*(t - 1); 
    N4s=(s/4 + 1/4)*(t + 1) + ((t + 1)*(s + t - 1))/4; 

    % 关于 t 求导 
    N1t=(s/4 - 1/4)*(s - t + 1) - (s/4 - 1/4)*(t + 1); 
    N2t=-(s/4 - 1/4)*(t - 1) - (s/4 - 1/4)*(s + t + 1); 
    N3t=(s/4 + 1/4)*(t - s + 1) + (s/4 + 1/4)*(t - 1); 
    N4t=(s/4 + 1/4)*(t + 1) + (s/4 + 1/4)*(s + t - 1); 

    Nst=[N1s N1t;N2s N2t;N3s N3t;N4s N4t];
end