求助，matlab second derivative approximation,导数逼近

splelvis

clear all;
" l9 F4 K7 ?" x/ [nx=50;
) Z. a7 p- i* R. |) iny=30;
% @/ n( }2 V4 K0 [4 Ihx=pi/nx;
+ `5 X$ n$ ?/ Z3 F7 L* k$ Sx=linspace(0,pi,nx+1);
y=linspace(0,pi,ny+1);
x_plus_h=x+hx.*ones(1,nx+1);
( v( g' D& g. U! v- j9 Z8 |0 Q, Qx_minus_h=x-hx.*ones(1,nx+1);
for i=1:nx+1
    for j=1:ny+1
: ^: l' q( X/ G9 a3 ]9 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)
8 u) K" s7 I! @4 C2 c) w    end;
end;
[xx,yy]=meshgrid(x,y);
$ w3 c6 O& i& {: {surf(xx,yy,f_xx);
title('partial derivative w.r.t.xx')
，

- I* l# d  l6 s6 ]另开一个f9文件，
/ f  ^2 j. f2 T0 g- Pfunction l=f9(x,y)
" E" U( @) ?( b) t) c$ l# t, nl=exp(sin(x-y));
) Y$ {0 m9 K) I/ v! T
* s# s+ O: x" ]# z  z, R
然后出来说错误了，
??? Input argument "x" is undefined.

Error in ==> f9 at 2
l=exp(sin(x-y));
3 I' S: G& R/ }* q$ DError 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);

; n+ W1 U3 R( R; ~0 [2 P1 A5 o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~~~~~~~~~~~~~~~`