求助，matlab second derivative approximation,导数逼近

splelvis

clear all;
& U% R# D# V: F" S7 l0 inx=50;
( c0 E) l8 V$ @, |# hny=30;
7 R5 Z/ t# ?7 A* T! R* F: k" n: `hx=pi/nx;
x=linspace(0,pi,nx+1);
  Z' p. M. g5 ~, Z. ^6 Ny=linspace(0,pi,ny+1);
) o/ e8 ?. e7 A2 M6 b( D* \x_plus_h=x+hx.*ones(1,nx+1);
x_minus_h=x-hx.*ones(1,nx+1);
7 @$ U! @0 k" ?* O) e2 y/ ^( Afor i=1:nx+1
    for j=1:ny+1
, N1 r1 ~$ P4 I4 Z4 n        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;
$ j1 s7 J# e! L* Jend;
( L4 W  w8 w2 L* [% v3 M' [; q7 `[xx,yy]=meshgrid(x,y);
1 M; q' A9 Y5 Qsurf(xx,yy,f_xx);
- S8 U9 i. X$ s; Ztitle('partial derivative w.r.t.xx')
，
% o  V) u- Q* p" [% Z
另开一个f9文件，
( c/ B% p6 M: e1 p& n: D  zfunction l=f9(x,y)
: P4 \. M" V, z6 C8 `# ml=exp(sin(x-y));

4 e  `3 y  K8 a3 J) X/ ^
然后出来说错误了，
( e3 U& q. {" c0 i??? Input argument "x" is undefined.
2 ~1 U8 [( k7 n0 Y( {6 F3 Z
Error in ==> f9 at 2
, C: {: y$ d! ]" h) ll=exp(sin(x-y));
2 j& b) q: ]9 mError 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);
$ G* h  l6 R  t! h6 P9 ^7 r) r
% n$ ]- `4 f/ s/ c4 c- K& j% ^2 e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~~~~~~~~~~~~~~~`