function x=fsxhesse(f,a,b)
% fsxhesse函數(shù) 求函數(shù)的hesse矩陣；
% 本程序僅是簡單的求二次函數(shù)的hesse矩陣！；
% x=fsxhesse(f)為輸入函數(shù) f為二次函數(shù) x1,x2為自變量；

% fsx TJPU 2008.6.15

x1=a;x2=b;
fx=diff(f,'x1');     %求f對x1偏導(dǎo)數(shù)
fy=diff(f,'x2');     %求f對x2偏導(dǎo)數(shù)
fxx=diff(fx,'x1');   %求二階偏導(dǎo)數(shù) 對x1再對x1
fxy=diff(fx,'x2');   %求二階偏導(dǎo)數(shù) 對x1再對x2
fyx=diff(fy,'x1');   %求二階偏導(dǎo)數(shù) 對x2再對x1
fyy=diff(fy,'x2');   %求二階偏導(dǎo)數(shù) 對x2再對x2
fxx=subs(fxx);       %將符號變量轉(zhuǎn)化為數(shù)值
fxy=subs(fxy);
fyx=subs(fyx);
fyy=subs(fyy);
x=[fxx,fxy;fyx,fyy]; %求hesse矩陣