求助，matlab second derivative approximation,导数逼近

splelvis

clear all;
nx=50;
, o+ K4 T) w3 w' h. vny=30;
hx=pi/nx;
+ j+ U* n6 T1 o* ?; n) Y6 O- @x=linspace(0,pi,nx+1);
5 x; E) {9 j2 i0 Z# L1 d8 Dy=linspace(0,pi,ny+1);
4 u& u/ }* e: B( d5 d- yx_plus_h=x+hx.*ones(1,nx+1);
x_minus_h=x-hx.*ones(1,nx+1);
for i=1:nx+1
# w+ r) K. `6 j8 Y' s    for j=1:ny+1
3 ]' B( s$ Z3 P# E9 ^3 g) O4 q- p        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)
/ w" b- c$ M/ D9 ]    end;
3 l' J5 Z0 L( S# hend;
/ Z+ }1 d( ]8 C' b* j[xx,yy]=meshgrid(x,y);
surf(xx,yy,f_xx);
title('partial derivative w.r.t.xx')
2 j$ u& Y8 [8 ~9 M，
, |' @+ P, L" j* b: P
另开一个f9文件，
6 c2 T8 p: y/ e: _8 Yfunction l=f9(x,y)
8 J" V' q9 n0 p/ Z2 O/ s, O$ ml=exp(sin(x-y));
7 _. A: {. }5 N( F7 }0 z* {+ y8 c

然后出来说错误了，
9 k6 b8 c" Y0 @. F! B??? Input argument "x" is undefined.
- P  D2 v1 E/ s1 {
% F% B3 a# d3 e; \8 OError in ==> f9 at 2
9 [7 Y& x& p: k$ o+ w+ El=exp(sin(x-y));
Error in ==> partial_derivxx at 11
  L* U: i: D3 P* O5 ~' K8 w        f_xx(j,i)=(f9(x_plus_h(i),y(j))-2*f9+f9(x_minus_h(i),y(j)))./(hx.^2);

3 s! M" A2 H: }9 I* s各位要怎么改才对呢

splelvis

我自己找到了问题，f9应该是 f9(x(i),y(j))

douglas8j

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

splelvis

不好意思，我也觉得自己太粗心了

douglas8j

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