求助，matlab second derivative approximation,导数逼近

splelvis

clear all;
0 m. C$ l5 g) A/ Anx=50;
ny=30;
/ o2 x4 B" u! k+ j' k& t9 ghx=pi/nx;
' }" `, s% U  Q; H( i4 ~" ox=linspace(0,pi,nx+1);
y=linspace(0,pi,ny+1);
- w, @, N' U. u- n1 zx_plus_h=x+hx.*ones(1,nx+1);
1 ?0 S1 B: ^, }  L/ S' N! ?$ Sx_minus_h=x-hx.*ones(1,nx+1);
1 ^5 l' _. i7 G5 F& _) N) w- C% tfor i=1:nx+1
! a) K  N1 T1 \8 L0 L+ m3 g2 d% b! ^    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& d# L. G( W8 R3 {    end;
end;
4 {$ s; ~) E$ P0 A) J. x1 a: p& k8 {[xx,yy]=meshgrid(x,y);
: o, z  \( H1 U) U9 k, B1 psurf(xx,yy,f_xx);
4 D3 |$ j; z4 m! |& Ptitle('partial derivative w.r.t.xx')
，
' d5 y. t3 I. z- U# G; L
另开一个f9文件，
7 x  q4 f1 Y$ \& Z8 Z0 t" Efunction l=f9(x,y)
: u+ v  M9 N6 E! Jl=exp(sin(x-y));


然后出来说错误了，
??? Input argument "x" is undefined.

' f. p. ~8 z4 j$ `Error in ==> f9 at 2
l=exp(sin(x-y));
- d# ]: [; g8 ?1 eError in ==> partial_derivxx at 11
4 |. g- l5 M- O        f_xx(j,i)=(f9(x_plus_h(i),y(j))-2*f9+f9(x_minus_h(i),y(j)))./(hx.^2);
$ h; ~2 H) m8 R) l4 @4 \/ H0 d8 ?
; i! e  n) a" f/ H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~~~~~~~~~~~~~~~`