求助，matlab second derivative approximation,导数逼近

splelvis

clear all;
nx=50;
ny=30;
hx=pi/nx;
# _3 \* P- L- k4 M" G" X: Y! J0 xx=linspace(0,pi,nx+1);
y=linspace(0,pi,ny+1);
x_plus_h=x+hx.*ones(1,nx+1);
0 A+ _  D/ \& F  {( ux_minus_h=x-hx.*ones(1,nx+1);
for i=1:nx+1
4 G. r& _! `9 m; Y% _    for j=1:ny+1
7 `  z- L/ D% b# h' f        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)
1 R3 Q; H5 K6 ^* ^    end;
& p1 F. G9 {8 X! ~! `end;
[xx,yy]=meshgrid(x,y);
0 `2 `' Y$ b# P) Z( @/ p# Gsurf(xx,yy,f_xx);
title('partial derivative w.r.t.xx')
，

另开一个f9文件，
function l=f9(x,y)
l=exp(sin(x-y));

4 L9 B) n+ P$ W0 ]* l* u
3 w# K: D  n* [" M0 n然后出来说错误了，
4 O1 y# {' j/ T??? Input argument "x" is undefined.
! a0 b7 U7 _/ Y. G& Q( P9 o7 @
2 E, w( t% {* I! T1 m% x: S2 f/ jError in ==> f9 at 2
9 f9 H# f+ m; O; m' T& ul=exp(sin(x-y));
Error in ==> partial_derivxx at 11
. j% Q2 |* q/ G8 f+ I" Z0 d        f_xx(j,i)=(f9(x_plus_h(i),y(j))-2*f9+f9(x_minus_h(i),y(j)))./(hx.^2);

3 E$ }/ h' z4 l, k. m2 {2 \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~~~~~~~~~~~~~~~`