求助，matlab second derivative approximation,导数逼近

splelvis

clear all;
nx=50;
. s0 P2 |6 h- }5 {3 J3 h% Eny=30;
hx=pi/nx;
x=linspace(0,pi,nx+1);
y=linspace(0,pi,ny+1);
5 K6 U! N# E) J0 e9 m+ Nx_plus_h=x+hx.*ones(1,nx+1);
8 S: {: O5 K$ r% cx_minus_h=x-hx.*ones(1,nx+1);
for i=1:nx+1
    for j=1:ny+1
6 k+ C# ~- y- B  ^; p( e        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;
0 T4 A0 s  b" b1 r2 H; fend;
[xx,yy]=meshgrid(x,y);
# B& `" S$ b" c5 x2 M4 B7 Jsurf(xx,yy,f_xx);
title('partial derivative w.r.t.xx')
7 J5 h9 F* ^0 n/ G  q/ h: i- o，

另开一个f9文件，
function l=f9(x,y)
l=exp(sin(x-y));
8 H- S+ L* v8 U. L/ h4 N
( i! q$ a; b1 H) @+ \
# [7 N( ^% q5 i9 S) m, Q7 }然后出来说错误了，
??? Input argument "x" is undefined.

6 `, f/ N. ?6 C- \" i5 NError in ==> f9 at 2
( Q8 n  S& t+ _, D2 m$ l/ q0 nl=exp(sin(x-y));
: x# \1 \- t) b1 ?2 q, h* `3 h8 `4 [0 RError in ==> partial_derivxx at 11
' H: b; V9 R- N) E* _" K3 o* o        f_xx(j,i)=(f9(x_plus_h(i),y(j))-2*f9+f9(x_minus_h(i),y(j)))./(hx.^2);
! U. N. P; A8 {. F
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~~~~~~~~~~~~~~~`