纽带x1 x2 u1 s1
f = 9 * x1 ^ 2 - 18 * x1 * x2 + 13 * x2 ^ 2 - 4......
+ U1 *(x1 ^ 2 + x2 ^ 2 + 2 * x1 - 16 + s1 ^ 2);
a = diff(f,x1);
b =差异(f,x2);
c = diff(f,u1);
d =差异(f,s1);
U1 = 0;
eval(a)
eval(b)
eval(c)
eval(d)