function ke=ele_stiff_matrix(E_ID,Nodes,Elements,E,u,Width)
    ENodes(:,1) = Elements(E_ID,:); 
    iN = size(ENodes,1); 
    ke = zeros(2*iN,2*iN); 
    D=[E/(1-u^2),u*E/(1-u^2),0;
       u*E/(1-u^2),E/(1-u^2),0;
       0,0,E/(2*(1+u))];

    % 计算高斯积分点坐标 
    r = [-sqrt(1/3) sqrt(1/3)];             % 2*2 高斯积分点 
    s = [r(1) r(1) r(2) r(2)]; 
    t = [r(2) r(1) r(1) r(2)];              % 高斯积分点坐标 
    % 高斯积分计算单元刚度矩阵 
    for i=1:4 
        J = Jacobi(E_ID,s(i),t(i),Elements,Nodes);             % 雅可比矩阵 
        Nst = DiffShapeFun(s(i),t(i));        % 形函数关于自然坐标s,t求导 
        Nxy = zeros(8,2); 
        for j=1:8 
          Nxy(j,:) = (J\Nst(j,:)')';             % 形函数关于 x,y 求导=inv(J)*Nst 
        end 
        Bm = [Nxy(1,1) 0 Nxy(2,1) 0 Nxy(3,1) 0 Nxy(4,1) 0 Nxy(5,1) 0 Nxy(6,1) 0 Nxy(7,1) 0 Nxy(8,1) 0;
            0 Nxy(1,2) 0 Nxy(2,2) 0 Nxy(3,2) 0 Nxy(4,2) 0 Nxy(5,2) 0 Nxy(6,2) 0 Nxy(7,2) 0 Nxy(8,2);
            Nxy(1,2) Nxy(1,1) Nxy(2,2) Nxy(2,1) Nxy(3,2) Nxy(3,1) Nxy(4,2) Nxy(4,1) Nxy(5,2) Nxy(5,1) Nxy(6,2) Nxy(6,1) Nxy(7,2) Nxy(7,1) Nxy(8,2) Nxy(8,1)]; 
        ke = ke+det(J)*Bm'*D*Bm*Width;
  
    end 
end