求助，matlab second derivative approximation,导数逼近

splelvis

clear all;
nx=50;
0 N- A" F8 k$ R" d) H  Nny=30;
hx=pi/nx;
, `3 H: b8 R' d7 fx=linspace(0,pi,nx+1);
- p; L8 U- \- N! R6 j+ X# N  fy=linspace(0,pi,ny+1);
6 i; w4 S* n9 Y% Lx_plus_h=x+hx.*ones(1,nx+1);
8 B+ W5 f& X. o( ex_minus_h=x-hx.*ones(1,nx+1);
for i=1:nx+1
    for j=1:ny+1
# H5 v- `0 _& U5 L        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)
6 X$ [  n, K8 ~( F    end;
end;
. N1 s: `) S% A* z[xx,yy]=meshgrid(x,y);
6 ]6 |6 \( \) _% R3 Esurf(xx,yy,f_xx);
3 {# P! I* g7 l" s$ dtitle('partial derivative w.r.t.xx')
，

另开一个f9文件，
function l=f9(x,y)
4 C, A( q& |2 r7 e$ q! Hl=exp(sin(x-y));
" a- c/ ~% o& M+ y' f

) h) p/ ~" X, L然后出来说错误了，
  I( r0 F2 K& l$ d??? Input argument "x" is undefined.

Error 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);

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~~~~~~~~~~~~~~~`