求助，matlab second derivative approximation,导数逼近

splelvis

clear all;
nx=50;
9 c0 G/ w2 G3 a$ C7 B2 M( m: }ny=30;
9 D1 z- k  G" N+ v( q3 Ihx=pi/nx;
0 e- \% q- P5 G- F+ e  }x=linspace(0,pi,nx+1);
y=linspace(0,pi,ny+1);
x_plus_h=x+hx.*ones(1,nx+1);
* u  U7 f3 a0 q& ?x_minus_h=x-hx.*ones(1,nx+1);
- Z, v( b, \/ a  K% l! vfor i=1:nx+1
    for j=1:ny+1
        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;
% [1 o- s: ^1 @8 k2 oend;
[xx,yy]=meshgrid(x,y);
' {8 f2 `1 s+ ^3 l* q* r6 zsurf(xx,yy,f_xx);
title('partial derivative w.r.t.xx')
6 u& O! n7 t% `1 {9 S- x6 e+ h* [1 E，
3 u9 r, g1 |# q+ P' ?5 g% {  p
5 u$ c9 a' [; V" [7 l另开一个f9文件，
function l=f9(x,y)
: M, Q6 ^: ~1 e: o$ Pl=exp(sin(x-y));


' Q  `) N  Z1 N" {' w( R3 g然后出来说错误了，
??? Input argument "x" is undefined.

7 k" ]  O. Y; d$ |' {, O) v/ v5 QError in ==> f9 at 2
l=exp(sin(x-y));
Error in ==> partial_derivxx at 11
3 ?" Y5 D% G  X+ K1 ~/ x        f_xx(j,i)=(f9(x_plus_h(i),y(j))-2*f9+f9(x_minus_h(i),y(j)))./(hx.^2);
- _. D( r6 ~4 |+ R/ f% Z% ^0 M6 q
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~~~~~~~~~~~~~~~`