求助，matlab second derivative approximation,导数逼近

splelvis

clear all;
nx=50;
ny=30;
) l1 f% U+ I# L6 a; V+ ]hx=pi/nx;
; V0 y- z* V. ]  e/ ~; O% t$ E5 Ax=linspace(0,pi,nx+1);
y=linspace(0,pi,ny+1);
0 O% E8 C8 X) C' kx_plus_h=x+hx.*ones(1,nx+1);
. Z9 P2 `* p) S* B* d* rx_minus_h=x-hx.*ones(1,nx+1);
for i=1:nx+1
    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)
    end;
end;
[xx,yy]=meshgrid(x,y);
surf(xx,yy,f_xx);
title('partial derivative w.r.t.xx')
6 H( K9 ?, F" K5 ]8 `# ^，

另开一个f9文件，
% p9 R$ L9 t% ~function l=f9(x,y)
l=exp(sin(x-y));
3 Q+ z( M4 e, C
. R3 {% |$ q! S* N: r9 [( l0 Z0 j
" W) u0 ]; c1 w7 _1 w0 i5 a% C然后出来说错误了，
  P1 N* P2 O% r( P0 f??? Input argument "x" is undefined.

0 B* D! v5 D: q, ~% \) U' LError in ==> f9 at 2
l=exp(sin(x-y));
; c( f# u# l. O# ~' lError 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);
8 r( c% [1 _, S# T6 C
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~~~~~~~~~~~~~~~`