symcf -- 求符号多项式关于任一变量各阶的系数

% find the coefficient of each order of x in a polynomial f

function a=symcf(f,x)

i=1;

f1=f;

while(f1~=0)

    a(i)=subs(f1,x,0)/factorial(i-1);

    i=i+1;

    f1=diff(f1,x);

end