求助，matlab second derivative approximation,导数逼近

splelvis

clear all;
nx=50;
5 E! l- }7 a7 @0 a& cny=30;
hx=pi/nx;
( V/ f! @0 X5 }/ O; o; n& o+ O( \x=linspace(0,pi,nx+1);
  G3 i! A6 f$ M* G# c0 S& ty=linspace(0,pi,ny+1);
: P3 {% _: v- N, b2 h" ~x_plus_h=x+hx.*ones(1,nx+1);
- g2 S* `" H0 R7 B/ ?x_minus_h=x-hx.*ones(1,nx+1);
for i=1:nx+1
    for j=1:ny+1
3 w+ `( C% O3 \" A: `        f_xx(j,i)=(f9(x_plus_h(i),y(j))-2*f9+f9(x_minus_h(i),y(j)))./(hx.^2);   %原式f(x+hx,y)-2f(x,y)+f(x-hx,y)./(hx^2)
    end;
( s& q# Y4 v+ C! @end;
[xx,yy]=meshgrid(x,y);
surf(xx,yy,f_xx);
title('partial derivative w.r.t.xx')
，

另开一个f9文件，
( m; a) B3 o3 ]6 x+ _' Yfunction l=f9(x,y)
l=exp(sin(x-y));


; f; i0 h' w" v3 B7 {; }: d( g然后出来说错误了，
??? Input argument "x" is undefined.
3 U8 |' W7 B7 h( F, V
8 `7 ^* a4 f: L* ?# g. YError in ==> f9 at 2
l=exp(sin(x-y));
1 e& P! U$ g' x( R. G# }Error in ==> partial_derivxx at 11
) A5 p" X! @  `4 w7 M) X/ \        f_xx(j,i)=(f9(x_plus_h(i),y(j))-2*f9+f9(x_minus_h(i),y(j)))./(hx.^2);

; x* I0 W+ ?4 b, u2 j* h/ @' |各位要怎么改才对呢

douglas8j

henhaodeyipianwenzhang~~~~~~~~~~~~~~~`

splelvis

不好意思，我也觉得自己太粗心了

douglas8j

abc~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

splelvis

我自己找到了问题，f9应该是 f9(x(i),y(j))