求助，matlab second derivative approximation,导数逼近

splelvis

clear all;
nx=50;
ny=30;
7 R2 w& P5 g8 s1 u7 {hx=pi/nx;
x=linspace(0,pi,nx+1);
5 z1 C; j+ `/ @4 ~4 M+ l' A2 Xy=linspace(0,pi,ny+1);
# _9 n. m% R- |6 a: S/ o; t' dx_plus_h=x+hx.*ones(1,nx+1);
x_minus_h=x-hx.*ones(1,nx+1);
for i=1:nx+1
( s* U7 P) x% |! s- s$ x    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)
$ P& d7 M/ c, R4 U. l    end;
end;
[xx,yy]=meshgrid(x,y);
surf(xx,yy,f_xx);
& @7 ]$ o+ T3 a2 L% l8 A+ T5 w& Qtitle('partial derivative w.r.t.xx')
，

另开一个f9文件，
" I2 C$ u( ~0 e, W9 B9 G! Ifunction l=f9(x,y)
l=exp(sin(x-y));
; ^7 B! i% r" N1 P& X  A  r& x- W; {+ c
# O' f% L; z! ]# z( @8 K" B: N
然后出来说错误了，
7 e  O! l! e7 S  _& d: z4 m??? Input argument "x" is undefined.

! o- T! {1 N) w+ M( JError in ==> f9 at 2
l=exp(sin(x-y));
Error 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);
4 ]" O8 `% P) V+ L. u
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~~~~~~~~~~~~~~~`