求助，matlab second derivative approximation,导数逼近

splelvis

clear all;
nx=50;
' U# s4 {: w0 a& }1 u" pny=30;
0 I3 j" p/ q" V% Y1 z( h, Rhx=pi/nx;
; d* N" {* f6 }, q/ `x=linspace(0,pi,nx+1);
: H: \8 R& ]  a8 W# N( _; ?y=linspace(0,pi,ny+1);
x_plus_h=x+hx.*ones(1,nx+1);
9 d9 M7 g* x+ c% s: p' \: hx_minus_h=x-hx.*ones(1,nx+1);
* B5 [/ n9 m7 h3 hfor i=1:nx+1
5 R! R$ {8 H5 Y/ I/ p. u& `    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)
, Z0 D7 s  g. `5 n1 T    end;
) I8 |. z/ x, Q+ Wend;
3 G9 c/ `4 m( f  _- b' |) T( B[xx,yy]=meshgrid(x,y);
3 H7 ^/ g9 G8 X: [8 `9 J; A, Jsurf(xx,yy,f_xx);
title('partial derivative w.r.t.xx')
0 Z+ j, q+ C5 V3 ]% u9 M，
4 @. g  w  g9 m9 {
! V4 Z& ?9 Z; w另开一个f9文件，
  b' d$ t# O  f/ Ffunction l=f9(x,y)
l=exp(sin(x-y));
" V9 L8 U/ {# m4 L, }% q( G
; n# Q6 r8 }' K9 b& ^: j$ c
然后出来说错误了，
??? Input argument "x" is undefined.

& _5 f9 ?: b5 F+ C- i5 YError in ==> f9 at 2
l=exp(sin(x-y));
: d- h5 P! G8 Y: p* n) U( C' CError 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);
' I9 M" q' G1 S+ a
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~~~~~~~~~~~~~~~`