clear; syms x y;z=f(x);eq1=diff(z,x);eq2=diff(z,y);[x,y]=solve(eq1,eq2,'x','y');x=double(x);y=double(y);这样就求得驻点了A=diff(z,x,2);B=diff(diff(z,x),y);C=diff(z,y,2);再求二阶偏导，再根据判别法判断上面的驻点是否为极点
