求助，matlab second derivative approximation,导数逼近

splelvis

clear all;
nx=50;
ny=30;
& J) v' y- o( W3 L$ L/ Chx=pi/nx;
x=linspace(0,pi,nx+1);
8 G: T( a# H2 D7 Oy=linspace(0,pi,ny+1);
) D* d6 q; ]2 J7 c! }: Fx_plus_h=x+hx.*ones(1,nx+1);
9 e) Q/ E5 o; B% P" U  `& ^- x0 q5 Ex_minus_h=x-hx.*ones(1,nx+1);
0 m0 X* [3 z" A* n4 ]" Mfor 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;
7 @0 ?! m' J3 S. k% X) z- [end;
[xx,yy]=meshgrid(x,y);
surf(xx,yy,f_xx);
0 W7 i3 L7 ~5 F2 e' p: d9 b& A: Ytitle('partial derivative w.r.t.xx')
，

另开一个f9文件，
function l=f9(x,y)
l=exp(sin(x-y));
4 h; j0 d9 Y# X. o. k' {
1 Y4 x( v; I6 J. G- K( C& v7 i1 B* I
然后出来说错误了，
, x' f2 \5 t2 B2 w* l$ s/ H, Q??? Input argument "x" is undefined.
% ^) [0 y$ _: M; e  s# k
Error in ==> f9 at 2
l=exp(sin(x-y));
# `- M1 ~4 N# o1 \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);
$ F# H4 u' O+ `" J" T
0 C4 O6 c' O6 P! A. B$ |1 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~~~~~~~~~~~~~~~`