求助，matlab second derivative approximation,导数逼近

splelvis

clear all;
nx=50;
2 i! [5 b7 K* O, e! @ny=30;
" h  Z' O4 }+ A* Z, t' x5 D6 h% jhx=pi/nx;
* W3 G; [7 l) [5 Z6 z% }: R% xx=linspace(0,pi,nx+1);
3 F8 m1 Y' D+ H: c9 u8 @. c( z2 p  _5 y7 Cy=linspace(0,pi,ny+1);
$ q8 N/ M# o& I3 _x_plus_h=x+hx.*ones(1,nx+1);
9 N' r, \8 v3 F& a. {1 B% cx_minus_h=x-hx.*ones(1,nx+1);
for i=1:nx+1
0 u- \, a( {8 i* V$ M8 r+ f    for j=1:ny+1
- K  @% {* _8 ~        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)
; Q- u9 }6 X+ m3 v; {    end;
$ A4 I+ G; k* o! n% s% l3 `end;
0 f, ^8 J/ e# f- G[xx,yy]=meshgrid(x,y);
surf(xx,yy,f_xx);
title('partial derivative w.r.t.xx')
，

4 A1 {, b+ e. B另开一个f9文件，
( K# h. `2 ^- f+ E! D; n" u9 E6 Mfunction l=f9(x,y)
l=exp(sin(x-y));
- K% ^+ o9 ^; H" |- }( A/ x% R
7 b) F& {; \7 f9 \# X" A8 n
然后出来说错误了，
6 T; n2 a! E. N??? Input argument "x" is undefined.

Error in ==> f9 at 2
l=exp(sin(x-y));
6 A; c9 y; Q% hError in ==> partial_derivxx at 11
        f_xx(j,i)=(f9(x_plus_h(i),y(j))-2*f9+f9(x_minus_h(i),y(j)))./(hx.^2);

; m) C/ _0 t8 G/ [  [% T0 j, A) Z3 `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))