求助，matlab second derivative approximation,导数逼近

splelvis

clear all;
nx=50;
ny=30;
hx=pi/nx;
x=linspace(0,pi,nx+1);
! Y% d9 W! Q9 U: w0 fy=linspace(0,pi,ny+1);
9 _  y  P  t5 m' }- \2 y3 Wx_plus_h=x+hx.*ones(1,nx+1);
x_minus_h=x-hx.*ones(1,nx+1);
1 U+ J2 }3 H  X! C! \2 l% n( o( }( rfor i=1:nx+1
    for j=1:ny+1
9 A7 o; \" n3 _        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;
- d# s* H# @( W, kend;
[xx,yy]=meshgrid(x,y);
surf(xx,yy,f_xx);
title('partial derivative w.r.t.xx')
1 l( ~- v! y- Q; ?  s，
  y/ y$ K( o0 b) T; G$ c
. g5 {6 ^1 I% d! B, y" N另开一个f9文件，
function l=f9(x,y)
; b' u  ]) o! ]7 q# K. I. O- kl=exp(sin(x-y));
/ P- R3 f) O7 X( f

" ]( B+ j' r. b# ~5 C: y然后出来说错误了，
??? Input argument "x" is undefined.
- ^; |$ g; y( }, D/ V
Error in ==> f9 at 2
  ?9 Y* B9 k2 {1 X6 ]- Pl=exp(sin(x-y));
Error in ==> partial_derivxx at 11
5 G# E8 N' ~& P. \0 c* m        f_xx(j,i)=(f9(x_plus_h(i),y(j))-2*f9+f9(x_minus_h(i),y(j)))./(hx.^2);
. S5 ~; e+ q3 w9 B5 u6 B# y- 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~~~~~~~~~~~~~~~`